Effects of hydrogen on friction and wear of steels are studied by 3ball-on-disk sliding tests in three gaseous environments: hydrogen, dry air and nitrogen. With SUJ2 ball against SUS316L disk, the coefficient of friction and the specific wear are the highest in dry air. With SUJ2 ball against SUSS 16 disk, significant transfer of stainless steel on SUJ2 ball is observed in hydrogen and nitrogen. Thus the differences in the friction and wear behaviors depend on combination of the ball and disk materials, and it is likely that these differences in the present tests are ascribed to effects of oxygen rather than those of hydrogen.