Abstract: A method for determination of sdLDL-C in a reaction solution containing a surfactant that preferentially inhibits the reaction of sdLDL-C with enzymes for cholesterol measurement such as cholesterol ester hydrolase. In the method, the enzymes for cholesterol measurement act on a sample to eliminate HDL-C, VLDL-C, CM-C and LgLDL-C. A reagent that causes the reaction of sdLDL-C remaining in the reaction solution to form hydrogen peroxide or reduced coenzyme is then added, following which the formed hydrogen peroxide or reduced coenzyme is measured. The sdLDL-C concentration in the sample may be determined by comparing the measurement value with and a previously-prepared calibration curve.