The invention provides a memory management method, a memory storage device and a memory control circuit unit. The method comprises the steps of obtaining the service condition of a first entity unit for storing data from a host system in a rewritable non-volatile memory module; determining a first rule according to the service condition; and executing first operation according to the first rule, wherein the first operation comprises the step of storing first data from the host system into the first entity unit; and storing second data from the rewritable non-volatile memory module into the second entity body, wherein the first rule corresponds to a first ratio of the data volume of the first data to the data volume of the second data, and therefore, the data from the outside and the inside can be stably stored by the memory storage device.