A method and apparatus for decoding a signal in a communication system. The method and apparatus includes receiving a punctured codeword including information bit nodes and unpunctured parity bit nodes; analyzing the unpunctured parity bit nodes, and detecting at least one first block including the unpunctured parity bit nodes among a plurality of blocks each including parity bit nodes having the same importance among all parity bit nodes; and recovering said all parity bit nodes by serial-decoding parity bit nodes included in the first block according to decoding priorities of parity bit nodes, determined by reflecting the first block in a predetermined decoding priority determining algorithm.