A simple, rapid, and sensitive microplate assay method for determination of ubiquinone in cosmetic products has been developed and validated. This method is based on measuring reactive oxygen species (ROS) generated from the redox cycle of quinone using redox colorimetric reagent, 2-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT). The reaction with ROS converts INT to a formazan dye having a strong absorbance at 510 nm that is increased with increasing concentration of ubiquinone. On the basis of this reaction, we developed a microplate assay method that allows high-throughput measurement of ubiquinone. This method uses microplate reader for the measurement of absorbance and it can determine many samples at one time. Under the optimized conditions, the proposed method was linear in the range of 0.02-4 mu M and the limit of detection (blank + 3SD) was 14.8 nM. We applied the proposed method to determine ubiquinone contents in cosmetic products, and the measurement values were in good agreement with the indicated value. The proposed colorimetric method should be useful as a high-throughput analysis for quality management of ubiquinone containing products.