A memory module including a plurality of memory banks, a memory control unit, and a built-in self-test (BIST) control unit is provided. The memory banks store data. The memory control unit accesses the data in accordance with a system command. The BIST control unit generates a BIST command to the memory control unit when a BIST function is enabled in the memory module. While the system command accessing the data in a specific memory bank exists, the memory command control unit has the priority to execute the system command instead of the BIST command testing the specific memory bank. Memory reliability of a system including the memory module is enhanced without reducing the system effectiveness.