Steam reforming of dimethyl ether (DME) was carried out over combined solid acid-CuO based catalysts. The reaction proceeded via a successive two-step mechanism: hydration of DME to methanol over solid acids, followed by steam reforming of methanol to produce H-2 and CO2 over CuO based catalysts. Effective hydration catalysts were various zeolites including H-mordenite, SO42-/ZrO2, and WO3/ZrO2 whose acid strength was Ho less than or equal to 3.0 or lower. When H-mordenite was combined with CuO/CeO2 and Pd/CeO2, a high yield of H-2 was attained. However, Pd/CeO2 produced much CO. Combination of H-mordenite and 80 wt.% CuO/CeO2 produced H-2 at a rate of 71 mol kg (cat h)(-1). Metallic copper (Cu-0) was deduced to be the active species. The catalyst gradually lost its activity during the reaction. The cause of deactivation was not the deactivation of H-mordenite but the coke formation on copper species. (C) 2004 Elsevier B.V. All rights reserved.