Provided are a flash memory system and a data writing method thereof, the method including (a) transmitting a predetermined command and an address signal to a flash memory device included in the flash memory system, (b) transmitting data to the flash memory device, and (c) generating a parity code for the data and transmitting the parity code to the flash memory device, where the steps (b) and (c) are repeated twice or more; and where the data and the corresponding parity codes are written in a page buffer of the flash memory device irrespective of a data field and a spare field.