Provided is an H.264 decoding method and device for detection of Network Abstract Layer (NAL) unit error. The method includes calculating a total macroblock count for one picture, calculating a difference between a previous frame count and a current frame count, whenever a NAL unit is received, counting a macroblock count whenever decoding the macroblock, until the one picture is made complete, setting information indicating that one erroneous picture is made complete when the counted macroblock count is less than the total macroblock count and reporting that the one erroneous picture is made complete when the difference is greater than “0”.