The electrochemical behavior of oxygen (O2) superoxide ion (O2) couple was investigated with the aid of ultra micro electrode technique in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfone)imide room-temperature molten salt. The diffusion coefficient of O2 was (1.8 ± 0.2) × 10-6 cm2 s-1 at 25°C. The activation energy of the diffusion process of O2 was estimated to be 27 kJ mol-1 from the temperature dependence of the diffusion coefficient. The solubility of O2 in BMPTFSI was 14 mmol dm-3 at 25°C and decreased with an increase in temperature. The diffusion coefficient of O2- was 0.86 × 10 -6 cm2 s-1 at 25°C. The formal potential of O2 O2- couple was 1.13 V vs. ferrocene / ferrocenium.