A method for protecting data in damaged memory cells by dynamically switching memory mode is provided. The method is adapted to an electronic device having a memory, which has a memory controller and at least one memory module, each of which is consisted of a plurality of memory cells, and the memory cells are divided into a plurality of pages. A power-on self test is executed and a mirror memory mode is activated to protect the data in the memory modules. An uncorrectable error of each page of the memory modules is detected by the memory controller when an operating system reads the memory. If the uncorrectable error in one page is detected, the memory module having the page is determined as a damaged memory module, and the mirror memory mode is switched to a spare memory mode, so as to protect the data in the memory modules.