Nano structured metal oxides including TiO2, Co3O4 and Fe3O4 have been synthesized and evaluated for their photocatalytic activity for hydrogen generation. The photocatalytic activity of nano cobalt oxide was then compared with two other nano structured metal oxides namely TiO2 and Fe3O4. The synthesized nano cobalt oxide was characterized thoroughly with respect to EDX and TEM. The yield of hydrogen was observed to be 900, 2000 and 8275 mu mol h(-1) g(-1) of photocatalyst for TiO2, Co3O4 and Fe3O4 respectively under visible light. It was observed that the hydrogen yield in case of nano cobalt oxide was more than twice to that of TiO2 and the hydrogen yield of nano Fe3O4 was nearly four times as compared to nano Co3O4. The influence of various operating parameters in hydrogen generation by nano cobalt oxide was then studied in detail. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.