The effect of catalyst fluidization on the conversion of methane to syngas in methane reforming with CO2 and H2O in the presence of O-2 under pressurized conditions was investigated over Ni and Pt catalysts. Methane and CO conversion in the fluidized bed reactor was higher than those in the fixed bed reactor over Ni0.15Mg0.85O catalyst under 1.0 MPa. This reactor effect was dependent on the catalyst properties. Conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that this phenomenon is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor. Although serious carbon deposition was observed on Ni0.15Mg0.85O in the fixed bed reactor, it was inhibited in the fluidized bed reactor.