diff --git a/tests/test_cache_system.py b/tests/test_cache_system.py
index 436c2d58b..fd1f812ca 100644
--- a/tests/test_cache_system.py
+++ b/tests/test_cache_system.py
@@ -490,6 +490,96 @@ def test_file_cache_uses_default_ttl_when_omitted(monkeypatch):
     assert AsyncFileCache().ttl == 7 * 24 * 3600
 
 
+def test_memory_backend_supports_per_key_ttl():
+    """
+    同一 region 的 key 应按各自 TTL 过期，不受首个 key 的 TTL 影响。
+    """
+    region = "per_key_ttl"
+    cache = MemoryBackend()
+    cache.set("short", "short-value", ttl=10, region=region)
+    cache.set("long", "long-value", ttl=20, region=region)
+    region_cache = MemoryBackend._region_caches[cache.get_region(region)]
+    started_at = region_cache.timer()
+
+    region_cache.expire(time=started_at + 11)
+
+    assert cache.get("short", region=region) is None
+    assert cache.get("long", region=region) == "long-value"
+    assert list(cache.items(region=region)) == [("long", "long-value")]
+
+
+def test_memory_backend_resets_ttl_when_key_is_rewritten():
+    """
+    重写已有 key 时应从重写时刻按新 TTL 重新计算过期时间。
+    """
+    region = "rewrite_per_key_ttl"
+    cache = MemoryBackend()
+    cache.set("key", "old", ttl=10, region=region)
+    region_cache = MemoryBackend._region_caches[cache.get_region(region)]
+    started_at = region_cache.timer()
+
+    cache.set("key", "new", ttl=20, region=region)
+    region_cache.expire(time=started_at + 11)
+
+    assert cache.get("key", region=region) == "new"
+
+    region_cache.expire(time=started_at + 21)
+
+    assert cache.get("key", region=region) is None
+
+
+def test_memory_backend_instances_share_region_with_per_key_ttl():
+    """
+    多个 backend 仍共享 region 数据，但每次写入的显式 TTL 应独立生效。
+    """
+    region = "shared_per_key_ttl"
+    first = MemoryBackend()
+    second = MemoryBackend()
+    first.set("first", "first-value", ttl=10, region=region)
+    second.set("second", "second-value", ttl=20, region=region)
+    region_cache = MemoryBackend._region_caches[first.get_region(region)]
+    started_at = region_cache.timer()
+
+    region_cache.expire(time=started_at + 11)
+
+    assert second.get("first", region=region) is None
+    assert first.get("second", region=region) == "second-value"
+
+
+def test_async_memory_backend_supports_per_key_ttl():
+    """
+    异步代理路径应与同步 backend 共享 region，并保留每个 key 的 TTL。
+    """
+    async def run_test():
+        region = "async_per_key_ttl"
+        sync_cache = MemoryBackend()
+        async_cache = AsyncMemoryBackend()
+        await async_cache.set("short", "short-value", ttl=10, region=region)
+        sync_cache.set("long", "long-value", ttl=20, region=region)
+        region_cache = MemoryBackend._region_caches[sync_cache.get_region(region)]
+        started_at = region_cache.timer()
+        region_cache.expire(time=started_at + 11)
+
+        assert await async_cache.get("short", region=region) is None
+        assert await async_cache.get("long", region=region) == "long-value"
+
+    asyncio.run(run_test())
+
+
+def test_memory_lru_backend_keeps_capacity_eviction_behavior():
+    """
+    per-key TTL 改造不应影响 LRU region 的容量淘汰行为。
+    """
+    region = "memory_lru"
+    cache = MemoryBackend(cache_type="lru", maxsize=2)
+    cache.set("first", 1, region=region)
+    cache.set("second", 2, region=region)
+    cache.set("third", 3, region=region)
+
+    assert cache.get("first", region=region) is None
+    assert list(cache.items(region=region)) == [("second", 2), ("third", 3)]
+
+
 def test_redis_original_key_decodes_quoted_key():
     """
     Redis items 返回的 key 应还原为原始缓存 key，确保带特殊字符的 key 可继续删除。