diff --git a/CHANGES.md b/CHANGES.md
index 5ec4f7a5be5..3dd30054dcc 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -80,6 +80,9 @@ To be released.
     a high latency internet connection.  [[#709]]
  -  `Swarm<T>.BootstrapAsync()` became to report `PeerDiscoveryException`
     instead of `SwarmException` directly. [[#604], [#726]]
+ -  `BlockChain<T>.Append()` became to unstage the staged `Transaction<T>`s
+    that have lower nonce than the highest nonce of the same signer's transactions
+    in the same chain, since these virtually never become valid.  [[#721], [#728]]
 
 ### Bug fixes
 
@@ -116,9 +119,11 @@ To be released.
 [#709]: https://github.com/planetarium/libplanet/pull/709
 [#718]: https://github.com/planetarium/libplanet/pull/718
 [#719]: https://github.com/planetarium/libplanet/pull/719
+[#721]: https://github.com/planetarium/libplanet/issues/721
 [#725]: https://github.com/planetarium/libplanet/pull/725
 [#726]: https://github.com/planetarium/libplanet/pull/726
 [#727]: https://github.com/planetarium/libplanet/pull/727
+[#728]: https://github.com/planetarium/libplanet/pull/728
 
 
 Version 0.7.0
diff --git a/Libplanet.Tests/Blockchain/BlockChainTest.cs b/Libplanet.Tests/Blockchain/BlockChainTest.cs
index 5cc53966c9f..dc380da2fa5 100644
--- a/Libplanet.Tests/Blockchain/BlockChainTest.cs
+++ b/Libplanet.Tests/Blockchain/BlockChainTest.cs
@@ -460,6 +460,64 @@ await Assert.ThrowsAsync<UnexpectedlyTerminatedActionException>(async () =>
             Assert.Equal(1, blockChain.Count);
         }
 
+        [Fact]
+        public void UnstageAfterAppendComplete()
+        {
+            DumbAction.RenderRecords.Value = ImmutableList<RenderRecord>.Empty;
+            MinerReward.RenderRecords.Value = ImmutableList<RenderRecord>.Empty;
+
+            PrivateKey privateKey = new PrivateKey();
+            (Address[] addresses, Transaction<DumbAction>[] txs) =
+                MakeFixturesForAppendTests(privateKey);
+            var genesis = _blockChain.Genesis;
+
+            try
+            {
+                Block<DumbAction> block1 = TestUtils.MineNext(
+                    genesis,
+                    miner: addresses[4],
+                    difficulty: _blockChain.Policy.GetNextBlockDifficulty(_blockChain),
+                    blockInterval: TimeSpan.FromSeconds(10));
+                _blockChain.Append(block1);
+                Assert.Empty(_blockChain.GetStagedTransactionIds());
+                _blockChain.StageTransactions(txs.ToImmutableHashSet());
+                Assert.Equal(2, _blockChain.GetStagedTransactionIds().Count);
+
+                Block<DumbAction> block2 = TestUtils.MineNext(
+                    block1,
+                    ImmutableHashSet<Transaction<DumbAction>>.Empty.Add(txs[0]),
+                    difficulty: _blockChain.Policy.GetNextBlockDifficulty(_blockChain),
+                    blockInterval: TimeSpan.FromSeconds(10)
+                );
+                _blockChain.Append(block2);
+                Assert.Equal(1, _blockChain.GetStagedTransactionIds().Count);
+                _blockChain.StageTransactions(txs.ToImmutableHashSet());
+                Assert.Equal(1, _blockChain.GetStagedTransactionIds().Count);
+
+                var actions = new[] { new DumbAction(addresses[0], "foobar") };
+                Transaction<DumbAction>[] txs2 =
+                {
+                    _fx.MakeTransaction(actions, privateKey: privateKey, nonce: 0),
+                };
+                _blockChain.StageTransactions(txs2.ToImmutableHashSet());
+                Assert.Equal(2, _blockChain.GetStagedTransactionIds().Count);
+
+                Block<DumbAction> block3 = TestUtils.MineNext(
+                    block2,
+                    ImmutableHashSet<Transaction<DumbAction>>.Empty.Add(txs[1]),
+                    difficulty: _blockChain.Policy.GetNextBlockDifficulty(_blockChain),
+                    blockInterval: TimeSpan.FromSeconds(10)
+                );
+                _blockChain.Append(block3);
+                Assert.Empty(_blockChain.GetStagedTransactionIds());
+            }
+            finally
+            {
+                DumbAction.RenderRecords.Value = ImmutableList<RenderRecord>.Empty;
+                MinerReward.RenderRecords.Value = ImmutableList<RenderRecord>.Empty;
+            }
+        }
+
         [Fact]
         public async Task RenderAfterAppendComplete()
         {
@@ -1750,7 +1808,7 @@ void BuildIndex(Guid id, Block<DumbAction> block)
         }
 
         private (Address[], Transaction<DumbAction>[])
-            MakeFixturesForAppendTests()
+            MakeFixturesForAppendTests(PrivateKey privateKey = null)
         {
             Address[] addresses =
             {
@@ -1761,7 +1819,7 @@ void BuildIndex(Guid id, Block<DumbAction> block)
                 _fx.Address5,
             };
 
-            PrivateKey privateKey = new PrivateKey(new byte[]
+            privateKey = privateKey ?? new PrivateKey(new byte[]
             {
                 0xa8, 0x21, 0xc7, 0xc2, 0x08, 0xa9, 0x1e, 0x53, 0xbb, 0xb2,
                 0x71, 0x15, 0xf4, 0x23, 0x5d, 0x82, 0x33, 0x44, 0xd1, 0x16,
diff --git a/Libplanet/Blockchain/BlockChain.cs b/Libplanet/Blockchain/BlockChain.cs
index f9d2be247d8..c8ffad25cc9 100644
--- a/Libplanet/Blockchain/BlockChain.cs
+++ b/Libplanet/Blockchain/BlockChain.cs
@@ -767,12 +767,26 @@ bool renderActions
                         Hash = block.Hash,
                     };
                     TipChanged?.Invoke(this, tipChangedEventArgs);
-                    ISet<TxId> txIds = block.Transactions
-                        .Select(t => t.Id)
-                        .ToImmutableHashSet();
 
                     _logger.Debug("Unstaging transactions...");
 
+                    ImmutableDictionary<Address, long> maxNonces = block.Transactions
+                        .GroupBy(
+                            t => t.Signer,
+                            t => t.Nonce,
+                            (signer, nonces) => new
+                            {
+                                signer = signer,
+                                maxNonce = nonces.Max(),
+                            }
+                        )
+                        .ToImmutableDictionary(t => t.signer, t => t.maxNonce);
+                    ISet<TxId> txIds = Store.IterateStagedTransactionIds()
+                        .Select(Store.GetTransaction<T>)
+                        .Where(tx => maxNonces.TryGetValue(tx.Signer, out long nonce) &&
+                            tx.Nonce <= nonce)
+                        .Select(tx => tx.Id)
+                        .ToImmutableHashSet();
                     Store.UnstageTransactionIds(txIds);
                     _logger.Debug("Block {blockIndex}: {block} is appended.", block?.Index, block);
                 }