A data protecting method and a memory storage device are provided. The data protecting method includes reading a first string from the rewritable non-volatile memory module to obtain a data string; performing a decoding operation based on the data string to obtain block information corresponding to a plurality of physical erasing units; inputting the block information to an error checking and correcting (ECC) circuit of the memory storage device to generate a second string; and storing the second string into the rewritable non-volatile memory module.