O-2 acts as a nonconsumed activator for gold nanoparticles (AuNPs) in the oxidation of hydrosilanes to silanols with water under O-2 atmosphere, providing an acceleration of more than 200 times relative to the reaction rate under Ar atmosphere. The AuNP catalyst under aerobic conditions exhibits high activity in the oxidation with high turnover numbers (1230000). Various hydrosilanes including less-reactive bulky ones can be converted to the corresponding silanols in excellent yields. Moreover, the present AuNP catalyst is reusable while maintaining the high performance.