diff --git a/README.md b/README.md
index 048a0c05..96ce0772 100644
--- a/README.md
+++ b/README.md
@@ -83,12 +83,12 @@
 - [x] Index
   - [x] Hash Index
     - Hash index can be used only equal(=) operator is specified to index having columns
-    - Access is serialized (not parallel)
+    - Thread safe but serialized (not supported concurrent access)
   - [x] SkipList Index
-    - Alternative of B-tree Index
-    - Parallel accesible
-  - [ ] B-tree Index
-    - Implementing now with [bltree-go-for-embedding](https://github.com/ryogrid/bltree-go-for-embedding) lib
+    - Concurrent access is supported
+  - [x] B-tree Index [^1]
+    - Using [bltree-go-for-embedding](https://github.com/ryogrid/bltree-go-for-embedding) lib
+    - Concurrent access is supported
   - [ ] Logging And Recovery Of Index Data
 - [ ] JOIN
   - [x] INNER JOIN (Hash Join, Index Join, Nested Loop Join)
diff --git a/lib/container/btree/btree_iterator.go b/lib/container/btree/btree_iterator.go
deleted file mode 100644
index 13840682..00000000
--- a/lib/container/btree/btree_iterator.go
+++ /dev/null
@@ -1,61 +0,0 @@
-package btree
-
-import (
-	"github.com/ryogrid/SamehadaDB/lib/samehada/samehada_util"
-	"github.com/ryogrid/SamehadaDB/lib/storage/buffer"
-	"github.com/ryogrid/SamehadaDB/lib/storage/index/index_common"
-	"github.com/ryogrid/SamehadaDB/lib/storage/page"
-	"github.com/ryogrid/SamehadaDB/lib/storage/page/skip_list_page"
-	"github.com/ryogrid/SamehadaDB/lib/types"
-	blink_tree "github.com/ryogrid/bltree-go-for-embedding"
-)
-
-type BTreeIterator struct {
-	bltr          *blink_tree.BLTree
-	bpm           *buffer.BufferPoolManager
-	curNode       *skip_list_page.SkipListBlockPage
-	curEntry      *index_common.IndexEntry
-	rangeStartKey *types.Value
-	rangeEndKey   *types.Value
-	keyType       types.TypeID
-	entryList     []*index_common.IndexEntry
-	curEntryIdx   int32
-}
-
-func NewSkipListIterator(bltr *blink_tree.BLTree, rangeStartKey *types.Value, rangeEndKey *types.Value) *BTreeIterator {
-	ret := new(BTreeIterator)
-
-	// TODO: (SDB) need to implement this
-	panic("Not implemented yet")
-	//headerPage := sl.getHeaderPage()
-	//
-	//ret.sl = sl
-	//ret.bpm = sl.bpm
-	//
-	//ret.rangeStartKey = rangeStartKey
-	//ret.rangeEndKey = rangeEndKey
-	//ret.keyType = headerPage.GetKeyType()
-	//ret.entryList = make([]*skip_list_page.IndexEntry, 0)
-	//
-	//ret.initRIDList(sl)
-
-	return ret
-}
-
-func (itr *BTreeIterator) initRIDList(bltr *blink_tree.BLTree) {
-	// TODO: (SDB) need to implement this
-	panic("Not implemented yet")
-}
-
-func (itr *BTreeIterator) Next() (done bool, err error, key *types.Value, rid *page.RID) {
-	// TODO: (SDB) need to implement this
-	panic("Not implemented yet")
-	if itr.curEntryIdx < int32(len(itr.entryList)) {
-		ret := itr.entryList[itr.curEntryIdx]
-		itr.curEntryIdx++
-		tmpRID := samehada_util.UnpackUint64toRID(ret.Value)
-		return false, nil, samehada_util.GetPonterOfValue(ret.Key), &tmpRID
-	} else {
-		return true, nil, nil, nil
-	}
-}