A transmitter is provided, which includes: an encoder configured to generate a low density parity check (LDPC) codeword comprising information word bits, first parity bits and second parity bits based on a parity check matrix; an interleaver configured to interleave the LDPC codeword; and a constellation mapper configured to map the interleaved LDPC codeword on constellation points, wherein the first parity bits are generated based on one of parity submatrices constituting the parity check matrix and the second parity bits are generated based on another of the parity submatrices constituting the parity check matrix.