The photocatalytic degradation of methylene blue water solution was carried out by irradiating microwave and UV light simultaneously using TiO2 photocatalyst balls prepared by Chemical Vapor Deposition method. A microwave-discharged electrodeless UV lamp was developed to use microwave and UV simultaneously for photocatalytic reactions. The results of photocatalytic degradation of methylene blue showed that the decomposition rate increased with the microwave intensity, the circulating fluid velocity and auxiliary oxidizing agents added. Especially, the rate constant of H2O2-added photocatalytic reaction increased about three times from 0.0061 min^(-1) to 0.0197 min^(-1) when microwave was additionally irradiated. This study demonstrates that the microwave irradiation can play a very important role in photocatalytic degradation using peroxides although it is not easy to quantitatively assess the effect of microwave on photocatalytic reactions from the experimental data of this study.