Water splitting with H2O/Zn/Fe3O4 reaction system is suggested for H-2 generation in order to utilize concentrated solar heat. This system has the possibility of generating more H-2 per 1 mol of Zn than Zn/H2O reaction system at the same temperature, which is noted recently. When a mixture of Zn and FC3O4 was heated to 873 K and steam was passed through, H-2 was obtained in 93.4% of the theoretical yield. The formation of Zn-ferrites with high content of zinc (ZnxFe3-xO4; 0.2 less than or equal to x less than or equal to 1) and ZnO was determined by XRD and Mossbauer spectroscopy. The yield of ZnO was 26-29%, which shows that the ratio of the competition-reaction (Zn/H2O system) has less effects on the total H-2 yield. The stoichiometry and the reaction mechanism of the system are discussed upon the analyses for the solid product.