In a cyclic code decoding method, a decoder analyzes a received codeword to identify unreliable symbols in the codeword, and sets candidate syndrome patterns accordingly. Then, a syndrome calculator calculates evaluated syndrome values associated with one of the candidate syndrome patterns, and an error location polynomial (ELP) generator generates an ELP according to the syndrome values. An error correction device corrects the errors in the codeword according to the ELP when a degree of the ELP is not more than a threshold value, and the syndrome calculator adjusts the syndrome values and the ELP generator generates another ELP according to the adjusted syndrome values when otherwise.