A decoding method, a memory storage device and a rewritable non-volatile memory module are provided. The method includes: reading a plurality of bits from the rewritable non-volatile memory module according to a reading voltage; performing a parity check of a low density parity check (LDPC) algorithm on the bits to obtain syndromes, and each of the bits is corresponding to at least one of the syndromes; determining whether the bits have an error according to the syndromes; if the bits have the error, obtaining a syndrome weight of each of the bits according to the syndromes corresponding to each of the bits; obtaining an initial value of each of the bits according to the syndrome weight of each of the bits; and performing a first iteration decoding of the LDPC algorithm on the bits according to the initial values. Accordingly, the decoding speed is increased.