Abstract: This paper reports the results of a study devoted to the hydrogen production from liquid water on Co_3O_4/SrTiO_3 powders under UV irradiation. The results indi- cated that the photocatalysts behave rather actively in alkali solution. A strong con- centration dependence of OH~- for the rate of H_2 formation was observed. Reduction pretreatment of the photocatalysts by H_2 is unfavourable for the H_2 production, but an oxidation pretreatment by O_2 may improve remarkably the catalytic effi- ciency. By using SPV technique and ESR, it is found that near and above valence band of SrTiO_3 the photocatalysts have band-gap surface states, which may associate with surface cobalt ions. We believe that the surface states play a key role in the charge separation and transfer processes. Finally, a mechanism model is proposed.