The solar H-2 generation with the oxygen deficiency of Al-Cu ferrite (AlaCubFecO4, 3a + b + 3c = 8) has been studied for application to conversion of solar thermal energy to chemical energy of H-2. The Al-Cu ferrite was newly synthesized with different Al:Cu:Fe mole ratios from the co-precipitate of their nitrates. The Al-Cu ferrite (Al:Cu:Fe mole ratios = 0.43:0.43:2.14) prepared at 1473 K was the single phase of the spinel type compound. The cyclic two-step water splitting reactions (02 releasing and H-2 generation reactions) using the Al-Cu ferrite (Al:Cu:Fe = 0.43:0.43:2.14) gave the O-2 and H-2 yields of 1.6 and 0.37%, respectively. In the 02 releasing reaction, the Al-Cu ferrite changes to the oxygen deficient form of spinel structure. The temperature (T = 1673 K) of the O-2 releasing reaction with Al-Cu ferrite was lowered by ca. 100 K than those of Zn ferrite and Ni ferrite systems. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.