An error correction circuit includes an error correction code (ECC) encoder and an ECC decoder. The ECC encoder generates, based on a main data, a parity data using an ECC represented by a generation matrix and stores a codeword including the main data and the parity data in a target page. The ECC decoder reads the codeword from the target page as a read codeword based on an externally provided address to generate different syndromes based on the read codeword and a parity check matrix which is based on the ECC, and applies the different syndromes to the main data in the read codeword to correct a single bit error when the single bit error exists in the main data or to correct two bit errors when the two bit errors occur in adjacent two memory cells in the target page.