Provided are a transmitter and a method for transmitting a data block in a wireless communication system. The method comprises the following steps: encoding an information bit and generating a block coded with an NCBPSS bit; generating two sub-blocks by parsing the coded block; and transmitting the two sub-blocks to the transmitter. By preventing the bits that are contiguous to the encoding block from having continuous identical reliabilities on a signal constellation, the deterioration of the decoding performance of the transmitter can be prevented.