A memory storage device, a memory controller, and a method for identifying a valid data are provided. A rewritable non-volatile memory chip of the memory storage device includes physical blocks. Each of the physical blocks has physical pages. In the present method, logical blocks are configured and mapped to a portion of the physical blocks, wherein each of the logical blocks has logical pages. When a data to be written by a host system into a specific logical page is received, a substitute physical block is selected, the data is written into a specific physical page in the substitute physical block, and the address of a physical page in which a previous data corresponding to the specific logic page is written is recorded into the specific physical page. Thereby, a physical page containing the latest valid data can be identified among several physical pages corresponding to a same logical page.