Photocatalytic steam reforming of methane (CH4 + 2H(2)O -> 4H(2) + CO2) was examined over modified and Unmodified sodium tantalate photocatalysts around room temperature. The activity of the photocatalysts was much influenced by metal cation doped into the bulk of NaTaO3, the crystallites size of NaTaO3, and metal nanoparticles loaded oil the surface. The highest activity was obtained over the NaTaO3 doped with La3+, where a moderate amount of La3+ should substitute for Na+ without distorting the crystal structure of NaTaO3. The large crystallites size was a more important factor than the high surface area For higher photocatalytic activity of NaTaO3:La. These factors such as doping and large crystallites should increase the density and the mobility of the photoexcited carriers to improve the intrinsic photocatalytic activity. A moderate amount of Pt nanoparticles loaded oil NaTaO3:La most enhanced the activity among the examined metal particles, which would contribute to not only separation of excited electrons from holes and the successive hydrogen production but also methane activation during reaction with water Or holes. The heat treatment after the addition of Pt, which probably formed the practical metal-semiconductor junction, was required for a high and stable photocatalytic activity. The best photocatalyst, Pt/NaTaO3:La(2%), exhibited more than two times higher activity than Pt/TiO2 did. The photocatalytic reaction lasted for a long time without deactivation. The effect of reaction Conditions such as reaction temperature, feed gas composition, and light intensity on the catalytic performance W is systematically optimized, and the highest H-2 production rate reached 4.5 mu nol min(-1) (270 mu mol h(-1)), corresponding to 0.6% methane conversion and 11% water conversion, which exceeded the equilibrium conversion. The apparent quantum yield in the range of 240-270 nm for the hydrogen production was estimated to be 30% when the irradiation light intensity was 2 mW cm(-2), which was higher than that Of the photocatalytic water-splitting system employing NiO/NaTaO3:La.