Cyclohexane oxidation was operated in a continuously stirred tank reactor at system pressures of 0.6-1.0 MPa under an air-like O-2/N-2 atmosphere (rather than pure O-2). Catalytic performance was investigated over Au nanoparticles (size: 3-8 nm) hosted by SBA-15 as well as Au particles (> 60 nm) deposited on MCM-41, and high turnover frequencies of desired products were detected over the former. Based on intrinsic activities of representative catalysts, we derived a size-sensitivity feature of cyclohexane oxidation over Au particles.