Abstract: AIM: To develope an HPLC method for the study of plasma concentration-time curve of coenzyme Q₁₀ (CoQ₁₀) in human body. METHODS: Chromatography was performed on a Spherisorb C₁₈ column (25 cm×4.6 mm ID) with ethanol-water-acetic acid (98∶2∶0.7) as mobile phase. The detection wavelength was 275 nm. The internal standard was coenzyme Q₉ (CoQ₉). After deproteinization with ethanol, the plasma was extracted with n-hexane. RESULTS: A good linearity was obtained from 0.2～4.0 μg.ml^-1 of CoQ₁₀ in human plasma with a correlation coefficient of 0.9998. The extraction recovery was more than 90%. The plasma concentration-time curve of CoQ₁₀ of eight volunteers was determined by this method following a controlled clinical experiment. CONCLUSION: The established HPLC method was proved to be a good mehtod for the determination of CoQ₁₀ in human plasma. The experimental results showed that the human plasma concentration of endogenous CoQ₁₀ was (763.3±86.3) ng.ml^-1 and was affected by food and movement.