Abstract: A method for detecting or measuring homocysteine in a sample includes the steps of (a) reacting a D-amino acid present in a sample with a D-amino acid converting enzyme to convert the D-amino acid into a substance that does not serve as a substrate of D-amino acid oxidase or D-amino acid acetyltransferase; (b) reducing homocysteine in the sample with a thiol compound; (c) reacting the reduced homocysteine with a methyltransferase and a methyl donor to newly produce D-amino acid; and (d) reacting the produced D-amino acid with the D-amino acid oxidase or the D-amino acid acetyltransferase in the presence of an SH reagent to produce hydrogen peroxide, and color-developing the produced hydrogen peroxide by using an oxidative color-developing agent.