To improve the thermal stability of separators for lithium batteries, we have developed heat-resistant separator films based on ceramic powder. These ceramic powder based separators (CPS) consist of ceramic powder with binder resin. We used two different particle size powders of aluminum oxide (0.01 or 0.3μm). By mixing ceramic powder and resin at an appropriate content ratio, both types of CPS films satisfied needs for the heat-resistance. Furthermore, CPS film using 0.01μm powder showed excellent charge–discharge cycling properties when applied to lithium rechargeable batteries as a separator.