A data storage device utilized for storing a plurality of data includes a memory and a controller. The memory includes a plurality of blocks, and each of the blocks includes a plurality of physical pages. The controller is coupled to the memory and maps the logical pages to the physical pages of the memory. When the controller detects that a first logical page of the logical pages is a currently-used logical page, it detects whether or not the second logical page which belongs to the last logical page of the first logical page is a currently-used logical page in order to find what is truly the last currently-used logical page.