Rolling contact fatigue (RCF) tests were conducted with some greases under hydrogen and other gas environments. Flaking lives of rolling element bearings depend on chemical composition of grease and environmental gas. Lives in hydrogen were shorter than those in air and almost equal to those in argon. The lives for perfluoropolyether greases were longer than those for hydrocarbon greases with base oil of POE. Surface analyses suggested that reduction of flaking life mainly depended on the lubrication condition and surface reaction. On the other hand, in the case with PAO based hydrocarbon grease in hydrogen, flaking failure occurred on the ball surface which was opposite surface for almost all cases. In that case, possible reason for reduction of bearing life may be hydrogen emblittlement.