A method of verifying a program operation in a non-volatile memory device includes performing a program operation, verifying whether or not each of a plurality of program target memory cells is programmed to a voltage higher than a verifying voltage, counting a number of fail status bits in response to determining that a fail status memory cell is not programmed with a voltage higher than the verifying voltage based on the verified result, and setting data so that a plurality of page buffers each output a pass signal when the number of the fail status bits is smaller than a number of error correction code (ECC) processing bits.