diff --git a/ledis/const.go b/ledis/const.go
index 577464d..024e38c 100644
--- a/ledis/const.go
+++ b/ledis/const.go
@@ -22,6 +22,11 @@ const (
 	hExpMetaType
 	zExpType
 	zExpMetaType
+
+	binType
+	binMetaType
+	bExpType
+	bExpMetaType
 )
 
 const (
diff --git a/ledis/ledis.go b/ledis/ledis.go
index 6bf333a..b9731c2 100644
--- a/ledis/ledis.go
+++ b/ledis/ledis.go
@@ -33,6 +33,7 @@ type DB struct {
 	listTx *tx
 	hashTx *tx
 	zsetTx *tx
+	binTx  *tx
 }
 
 type Ledis struct {
@@ -114,6 +115,7 @@ func newDB(l *Ledis, index uint8) *DB {
 	d.listTx = newTx(l)
 	d.hashTx = newTx(l)
 	d.zsetTx = newTx(l)
+	d.binTx = newTx(l)
 
 	return d
 }
diff --git a/ledis/t_bin.go b/ledis/t_bin.go
new file mode 100644
index 0000000..044f6cf
--- /dev/null
+++ b/ledis/t_bin.go
@@ -0,0 +1,342 @@
+package ledis
+
+import (
+	"encoding/binary"
+	"errors"
+	"github.com/siddontang/ledisdb/leveldb"
+)
+
+const (
+	OPand byte = iota + 1
+	OPor
+	OPxor
+	OPnot
+)
+
+const (
+	segWidth uint32 = 9
+	segSize  uint32 = uint32(1 << segWidth) // byte
+
+	minSeq uint32 = 0
+	maxSeq uint32 = uint32((1 << 31) - 1)
+)
+
+var bitsInByte = [256]int32{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 1, 2, 2, 3, 2, 3, 3, 4, 2, 3, 3, 4, 3, 4, 4, 5, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 2, 3, 3, 4, 3, 4, 4, 5, 3, 4, 4, 5, 4, 5, 5, 6, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 3, 4, 4, 5, 4, 5, 5, 6, 4, 5, 5, 6, 5, 6, 6, 7, 4, 5, 5, 6, 5, 6, 6, 7, 5, 6, 6, 7, 6, 7, 7, 8}
+
+var errBinKey = errors.New("invalid bin key")
+var errOffset = errors.New("invalid offset")
+
+func getBit(sz []byte, offset uint32) uint8 {
+	index := offset >> 3
+	if index >= uint32(len(sz)) {
+		return 0 // error("overflow")
+	}
+
+	offset -= index << 3
+	return sz[index] >> offset & 1
+}
+
+func setBit(sz []byte, offset uint32, val uint8) bool {
+	if val != 1 && val != 0 {
+		return false // error("invalid val")
+	}
+
+	index := offset >> 3
+	if index >= uint32(len(sz)) {
+		return false // error("overflow")
+	}
+
+	offset -= index << 3
+	if sz[index]>>offset&1 != val {
+		sz[index] ^= (1 << offset)
+	}
+	return true
+}
+
+func (db *DB) bEncodeMetaKey(key []byte) []byte {
+	mk := make([]byte, len(key)+2)
+	mk[0] = db.index
+	mk[1] = binMetaType
+
+	copy(mk, key)
+	return mk
+}
+
+func (db *DB) bEncodeBinKey(key []byte, seq uint32) []byte {
+	bk := make([]byte, len(key)+8)
+
+	pos := 0
+	bk[pos] = db.index
+	pos++
+	bk[pos] = binType
+
+	binary.BigEndian.PutUint16(bk[pos:], uint16(len(key)))
+	pos += 2
+
+	copy(bk[pos:], key)
+	pos += len(key)
+
+	binary.BigEndian.PutUint32(bk[pos:], seq)
+
+	return bk
+}
+
+func (db *DB) bDecodeBinKey(bkey []byte) (key []byte, seq uint32, err error) {
+	if len(bkey) < 8 || bkey[0] != db.index {
+		err = errBinKey
+		return
+	}
+
+	keyLen := binary.BigEndian.Uint16(bkey[2:4])
+	if int(keyLen+8) != len(bkey) {
+		err = errBinKey
+		return
+	}
+
+	key = bkey[4 : 4+keyLen]
+	seq = uint32(binary.BigEndian.Uint16(bkey[4+keyLen:]))
+	return
+}
+
+func (db *DB) bParseOffset(key []byte, offset int32) (seq uint32, off uint32, err error) {
+	if offset < 0 {
+		if tailSeq, tailOff, e := db.bGetMeta(key); e != nil {
+			err = e
+			return
+		} else {
+			offset += int32(tailSeq<<segWidth | tailOff)
+			if offset < 0 {
+				err = errOffset
+				return
+			}
+		}
+	}
+
+	off = uint32(offset)
+
+	seq = off >> segWidth
+	off &= (segSize - 1)
+	return
+}
+
+func (db *DB) bGetMeta(key []byte) (tailSeq uint32, tailOff uint32, err error) {
+	var v []byte
+
+	mk := db.bEncodeMetaKey(key)
+	v, err = db.db.Get(mk)
+	if err != nil {
+		return
+	}
+
+	if v != nil {
+		tailSeq = binary.LittleEndian.Uint32(v[0:4])
+		tailOff = binary.LittleEndian.Uint32(v[4:8])
+	}
+	return
+}
+
+func (db *DB) bSetMeta(t *tx, key []byte, tailSeq uint32, tailOff uint32) {
+	ek := db.bEncodeMetaKey(key)
+
+	//	todo ..
+	//	if size == 0 // headSeq == tailSeq
+	//		t.Delete(ek)
+
+	buf := make([]byte, 8)
+	binary.LittleEndian.PutUint32(buf[0:4], tailSeq)
+	binary.LittleEndian.PutUint32(buf[4:8], tailOff)
+
+	t.Put(ek, buf)
+	return
+}
+
+func (db *DB) bUpdateMeta(t *tx, key []byte, seq uint32, off uint32) (tailSeq uint32, tailOff uint32, err error) {
+	if tailSeq, tailOff, err = db.bGetMeta(key); err != nil {
+		return
+	}
+
+	if seq > tailSeq || (seq == tailSeq && off > tailOff) {
+		db.bSetMeta(t, key, seq, off)
+		tailSeq = seq
+		tailOff = off
+	}
+	return
+}
+
+// func (db *DB) bDelete(key []byte) int64 {
+// 	return 0
+// }
+
+func (db *DB) BGet(key []byte) (data []byte, err error) {
+	if err = checkKeySize(key); err != nil {
+		return
+	}
+
+	var tailSeq, tailOff uint32
+	if tailSeq, tailOff, err = db.bGetMeta(key); err != nil {
+		return
+	}
+
+	var offByteLen uint32 = tailOff >> 3
+	if tailOff&7 > 0 {
+		offByteLen++
+	}
+
+	var dataCap uint32 = tailSeq<<3 + offByteLen
+	data = make([]byte, dataCap)
+
+	minKey := db.bEncodeBinKey(key, minSeq)
+	maxKey := db.bEncodeBinKey(key, tailSeq)
+	it := db.db.RangeLimitIterator(minKey, maxKey, leveldb.RangeClose, 0, -1)
+	for pos, end := uint32(0), uint32(0); it.Valid(); it.Next() {
+		end = pos + segSize
+		if end >= offByteLen {
+			end = offByteLen
+		}
+
+		copy(data[pos:end], it.Value())
+		pos = end
+	}
+	it.Close()
+
+	return
+}
+
+// func (db *DB) BDelete(key []byte) (int8, error) {
+
+// }
+
+func (db *DB) getSegment(key []byte, seq uint32) ([]byte, []byte, error) {
+	bk := db.bEncodeBinKey(key, seq)
+	segment, err := db.db.Get(bk)
+	if err != nil {
+		return bk, nil, err
+	}
+	return bk, segment, nil
+}
+
+func (db *DB) allocateSegment(key []byte, seq uint32) ([]byte, []byte, error) {
+	bk, segment, err := db.getSegment(key, seq)
+	if err == nil && segment == nil {
+		segment = make([]byte, segSize, segSize) // can be optimize ?
+	}
+	return bk, segment, err
+}
+
+func (db *DB) BSetBit(key []byte, offset int32, val uint8) (ori uint8, err error) {
+	if err = checkKeySize(key); err != nil {
+		return
+	}
+
+	//	todo : check offset
+	var seq, off uint32
+	if seq, off, err = db.bParseOffset(key, offset); err != nil {
+		return 0, err
+	}
+
+	var bk, segment []byte
+	if bk, segment, err = db.allocateSegment(key, seq); err != nil {
+		return 0, err
+	}
+
+	if segment != nil {
+		ori = getBit(segment, off)
+		setBit(segment, off, val)
+
+		t := db.binTx
+		t.Lock()
+		t.Put(bk, segment)
+		if _, _, e := db.bUpdateMeta(t, key, seq, off); e != nil {
+			err = e
+			return
+		}
+		err = t.Commit()
+		t.Unlock()
+	}
+
+	return
+}
+
+func (db *DB) BGetBit(key []byte, offset int32) (uint8, error) {
+	if seq, off, err := db.bParseOffset(key, offset); err != nil {
+		return 0, err
+	} else {
+		_, segment, err := db.getSegment(key, seq)
+		if err != nil {
+			return 0, err
+		}
+
+		if segment == nil {
+			return 0, nil
+		} else {
+			return getBit(segment, off), nil
+		}
+	}
+}
+
+// func (db *DB) BGetRange(key []byte, start int32, end int32) ([]byte, error) {
+// 	section := make([]byte)
+
+// 	return
+// }
+
+func (db *DB) BCount(key []byte, start int32, end int32) (cnt int32, err error) {
+	var sseq uint32
+	if sseq, _, err = db.bParseOffset(key, start); err != nil {
+		return
+	}
+
+	var eseq uint32
+	if eseq, _, err = db.bParseOffset(key, end); err != nil {
+		return
+	}
+
+	var segment []byte
+	skey := db.bEncodeBinKey(key, sseq)
+	ekey := db.bEncodeBinKey(key, eseq)
+
+	it := db.db.RangeLimitIterator(skey, ekey, leveldb.RangeClose, 0, -1)
+	for ; it.Valid(); it.Next() {
+		segment = it.Value()
+		for _, bit := range segment {
+			cnt += bitsInByte[bit]
+		}
+	}
+	it.Close()
+
+	return
+}
+
+// func (db *DB) BLen(key []) (uint32, error) {
+
+// }
+
+// func (db *DB) BOperation(op byte, dstkey []byte, srckeys ...[]byte) (int32, error) {
+// 	//	return :
+// 	//		The size of the string stored in the destination key,
+// 	//		that is equal to the size of the longest input string.
+// 	if op < OPand || op > OPnot {
+// 		return
+// 	}
+
+// }
+
+// func (db *DB) BExpire(key []byte, duration int64) (int64, error) {
+
+// }
+
+// func (db *DB) BExpireAt(key []byte, when int64) (int64, error) {
+
+// }
+
+// func (db *DB) BTTL(key []byte) (int64, error) {
+
+// }
+
+// func (db *DB) BScan(key []byte, count int, inclusive bool) ([]KVPair, error) {
+
+// }
+
+// func (db *DB) bFlush() (drop int64, err error) {
+
+// }
diff --git a/ledis/t_bin_test.go b/ledis/t_bin_test.go
new file mode 100644
index 0000000..4a634cb
--- /dev/null
+++ b/ledis/t_bin_test.go
@@ -0,0 +1,58 @@
+package ledis
+
+import (
+	"testing"
+)
+
+func cmpBytes(a []byte, b []byte) bool {
+	if len(a) != len(b) {
+		return true
+	}
+
+	for i, n := range a {
+		if n != b[i] {
+			return true
+		}
+	}
+	return false
+}
+
+func TestBinary(t *testing.T) {
+	db := getTestDB()
+
+	key := []byte("test_bin")
+
+	if v, _ := db.BGetBit(key, 100); v != 0 {
+		t.Error(v)
+	}
+
+	if ori, _ := db.BSetBit(key, 50, 1); ori != 0 {
+		t.Error(ori)
+	}
+
+	if v, _ := db.BGetBit(key, 50); v != 1 {
+		t.Error(v)
+	}
+
+	if ori, _ := db.BSetBit(key, 50, 0); ori != 1 {
+		t.Error(ori)
+	}
+
+	if v, _ := db.BGetBit(key, 50); v != 0 {
+		t.Error(v)
+	}
+
+	db.BSetBit(key, 7, 1)
+	db.BSetBit(key, 8, 1)
+	db.BSetBit(key, 9, 1)
+	db.BSetBit(key, 10, 1)
+
+	if sum, _ := db.BCount(key, 0, -1); sum != 4 {
+		t.Error(sum)
+	}
+
+	data, _ := db.BGet(key)
+	if cmpBytes(data, []byte{0x80, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00}) {
+		t.Error(data)
+	}
+}