Aim To develop a reliable method for the measurement of serum lipoprotein(a) cholesterol.Methods Serum aliquots were centrifuged in the presence of proline at a density of 1.044 g/mL,the bottom fraction,which contains 95% of lipoprotein(a),was readjusted to density of 1.040 in the presence of mercaptoethanol and recentrifuged.Cholesterol levels in the ultracentrifugation top fractions [lipoprotein(a) cholesterol] were analyzed by high-performance liquid chromatography.Results Mercaptoethanol effectively dissociated lipoprotein(a) into apolipoprotein(a) and LDL-like lipoproteins [Lp(a-)].The dissociated Lp(a) showed a distinctive density distribution from that of the native lipoprotein(a).This finding enabled direct and reliable separation of lipoprotein(a) by ultracentrifugation.The with-in run and total CVs for the measurement of lipoprotein(a) cholesterol were 1.84%～2.17% and 2.85%～4.29%,respectively.Conclusion A new method for the measurement of lipoprotein(a) cholesterol by ultracentrifugation and high-performance liquid chromatography has been established.It is reliable and precise and may play an important role in standardization of lipoprotein(a) measurement.