An Al alloy ribbon with finer Al grains was prepared using a rapid spinning technique, and then was annealed at different temperatures to modify its microstructures, such as: Al grain size, size and number of Ga-In-Sn phase. The microstructures and phase compositions of the as-prepared and those annealed ribbons were investigated by means of XRD and SEM/EDX. The reaction of Al and the grain boundary phase was measured using DSC. Based on DSC analysis and other experiments, the formation of Al-Ga-In-Sn eutectic was suggested the origin of the alloy being capable of splitting water. Kinetic measurements found that the H-2 generation rate depends strongly on the microstructures of ribbons. An analytical expression was established to calculate the H-2 generation rates of ribbons with the measured microstructure parameters, and the calculated results agreed well with measurements. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.