A data processing method of a memory system including a flash memory, which includes judging whether data initially read from a selected page of the flash memory is correctable. If the initially read data is judged not to be correctable, the data is newly read from the selected page based upon each of newly determined read voltages. Thereafter, error-free sub-sectors of the newly read data are collected based upon EDC data corresponding to the initially read data. The data of the error-free sub-sectors are then corrected based upon ECC data corresponding to the initially read data.