By using hydrogen microprint technique (HMPT) , effect of microstructure on hydrogen permeation behavior in 7075 and 7475 aluminum alloys exposed to gaseous hydrogen has been investigated. The important findings are as follows. The amount of permeated hydrogen is strongly dependent on crystalline structure, temper and impurity content. Emission sites of hydrogen are constituent particles such as Al₇Cu₂Fe. The results indicate that subgrain boundaries and misfit dislocations present at the interface between stable η precipitate and the matrix can act as trapping sites for hydrogen. Invasion sites of hydrogen are presumed to be the constituent particles. From quantitative investigations on the amount of emitted hydrogen and on lattice diffusion of hydrogen, as well as from the above result that the subgrain boundaries act as trapping sites, migration of hydrogen is deduced to take place by grain boundary diffusion, not by lattice diffusion, nor by pipe diffusion along dislocations.