Provided are a flash memory system and a data reading method thereof, the method including serially reading groups of data and parity codes corresponding to each of the respective groups from a page buffer; calculating the parity for each serially read group; checking for errors in each serially read group by comparing each calculated parity with a corresponding serially read parity code, respectively; and providing an output signal indicative of any comparative parity errors detected, wherein the reading of each group of data is followed by the reading of the parity code for the group, and the checking for errors in each group of data is done during the serial reading operation.