A memory space management method adapted to a rewritable non-volatile memory module having a plurality of physical blocks is provided. In the memory space management method, a first area and a second area are configured. An authentication information is received from a host system, and whether the authentication information matches a predetermined authentication information is determined. If the authentication information does not match the predetermined authentication information, a counting value is updated. If the counting value matches a predetermined number, a first procedure is executed. In the first procedure, a third area is configured, wherein the capacity of the third area is a sum of the capacity of the first area and at least a portion of the capacity of the second area. The third area is provided to the host system to be accessed. Thereby, the memory space of the rewritable non-volatile memory module is effectively used.