Metal Al particle surfaces were modified by fine gamma-Al2O3 grains using a mixture of Al and Al(OH)(3) powders, which was pressureless sintered at a temperature of 600 degrees C in vacuum. All the constituents on original Al particle surfaces were transformed into gamma-Al2O3 phase after sintering. No dense passive oxide layers on Al particle surfaces were formed even after the modified Al particles were exposed to oxidation environment. The modified Al particles could continuously react with pure water and generate hydrogen at room temperature. The present finding implies that metal Al could become hydrogen-generation material by surface modification.