Objective: To study the interference and mechanism of vitamin C on determination of cholesterol and triglycerides. Methods: Cholesterol concentrations were determined with COD PAP method and triglycerides concentrations were determined with GPO PAP method. Results: When a series of samples containing the same concentration of lipids but different concentrations of vitamin C were determined, the determined cholesterol and triglycerides concentrations decreased with the increase of vitamin C concentrations in the sample. When lipid free hydrogen peroxide solutions were determined, the determined cholesterol and triglyceride concentrations decreased with dilutions of hydrogen peroxide. When hydrogen peroxide concentration remained constant in solutions , the determined cholesterol and triglyceride concentrations decreased with the increase of vitamin C concentrations in the solutions . Conclusion: Vitamin C can interfere with the determination of cholesterol with COD PAP method, and the determination of triglycerides with GPO PAP method, resulting in false lower cholesterol and triglyceride concentrations. Vitamin C interferes with the determination of cholesterol and triglycerides possibly through the reduction of the intermittent product hydrogen peroxide and final product quinoneimine.