Hydrogen permeation experiments were performed continuously over 45 hours on iron and steels (0.007-0.19%C) by an electrochemical method (nickel-plating method). The hydrogen was charged cathodically with a constant current density, 40A/m2, in two buffer solutions. The blisters were observed optically and electron scanning microscopically. The hydrogen diffusivity (D) and hydrogen content (C0) were kept constant during hydrogen permeation when an acetic buffer solution was used. However, D decreased and C0 increased with permeation time, when a boric buffer solution was used. In the latter, many blisters were formed in the specimens during the permeation, but there was no blister in the former because C0 was less than 0.1ppm. Blisters were formed at nonmetallic inclusions, Al2O3. These hydrogen permeation behaviors are discussed by the hydrogen trap effect at nonmetallic inclusions and at blisters around nonmetallic inclusions.