In this paper, the photocatalytic decomposition of azo dye reactive brilliant red X-313 was investigated in microwave assisted photocatalysis with microwave electrodeless lamp as light source (MWL/TiO2). A novel grain TiO2 (GTOl) rather than the well-known P25 TiO2 had been tested to determine whether its photocatalytic efficiency was good enough for use in water purification. The results showed that although GT01 was not so good as P25, it was easier separated from water and was more applicable. The effect of different operating parameters in MWL/TiO2 with GT01 as catalyst on photocatalytic oxidation was discussed. The photodegradation was favored with low initial pH, high temperature and high light intensity. The optimal amount of GT01 under our experimental condition was 4g/l. Some inorganic ions like CO32-, NO3- and SO42- also affected the photocatalytic efficiency. The order was CO32- > SO42- > NO3-. Moreover, microwave irradiation changed the effect of operating parameters. The effect of initial pH, reactant concentration, and dissolved oxygen was weakened, whereas the effect of temperature and light intensity was magnified. (c) 2005 Elsevier B.V. All rights reserved.