An improved bit mapping method and apparatus for a communication system is provided. A bit mapping method of the present invention includes arranging coded bits in a codeword in an order of recovery capability. A shift region including a number of coded bits is set. The coded bits are rearranged in the shift region by shifting the shift region by a number of bits equal to a number of bits that is indicated by a shift factor. The rearranged coded bits are mapped into a modulation symbol in an order of reliability from a lowest reliability bit position to a highest reliability bit position of the modulation symbol.