In this paper, I present the photocatalytic hydrogen production by using transition metal ions-doped gamma-Bi2O3 which is an oxide semiconductor having the band gap of 2.8 eV. gamma-Bi2O3 semiconductor was doped with various transition metal ions, Cr(VI), Fe(III), Co(II), Ni(II), Ru(III), Pd(II), etc., by the high-temperature sintering method and characterized by DRS, IR, SEM, TEM, XPS, and EPR. Photocatalytic hydrogen production was carried out by using methyl viologen as the electron relay by using xenon arc lamp as the light source. The photocatalytic hydrogen-production efficiency of the doped gamma-Bi2O3 with the different dopants is found to be in the decreasing order: Pd(II) > Ru(III) > Co(II) > Ni(Il) > Fe(III) > Cr(IV) > undoped gamma-Bi2O3. Two factors seem to be responsible for the effect of transition metal ions ex. Schottky type of barrier and metal ions behave as microcathodes. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.