A method for measuring a proportion of sA1c (%), which includes, when a peak derived from abnormal hemoglobin D, abnormal hemoglobin S or abnormal hemoglobin C is identified, calculation of the peak area, and measurement of the proportion of sA1c (%) corrected by using the calculation results. Results of measurement are obtained, by cation exchange chromatography, of sA1c (%) with a subject who provided a blood sample containing abnormal hemoglobin D, abnormal hemoglobin S or abnormal hemoglobin C by eliminating influences by such abnormal hemoglobin.