It is intended to provide a method of pre-treating a sample for measuring a saccharified amine to thereby enable highly reliable measurement of the saccharified amine. A saccharified amino acid in the sample is decomposed by treating with fructosyl amino acid oxidase FAOD, then the saccharified amine to be measured contained in the sample is treated with FAOD and the oxidation-reduction reaction is measured to thereby quantify the saccharified amine. The FAOD whereby the saccharified amino acid is treated and the FAOD whereby the saccharified amine is treated may have either the same or different substrate specificities. In case of using the same FAOD, the saccharified amino acid is decomposed by treating with the FAOD and then the FAOD is inactivated with a protease. At the same time, the saccharified amine is decomposed and the same FAOD is added to the decomposition product followed by the measurement of the oxidation-reduction reaction.