Understanding the processes of charge generation, transfer and capture is important for the design and synthesis of efficient photocatalysts. In this work, light-induced charge separation and effect of O₂ on electron transfer processes in SrTiO₃ were investigated by electron paramagnetic resonance (EPR). It was found that photoinduced electron transfer from O²⁻ to Ti⁴⁺ produced Ti³⁺ and O⁻ redox radical pairs under vacuum condition. Under oxygen atmosphere, however, surface bound superoxide radicals O₂⁻ were formed by electron reduction of adsorbed oxygen at initial photoirradiation stage, and quenched by the reverse electron transfer to Ti⁴⁺ upon further photoirradiation. Formation of long-lived charge separation associated [Ti³⁺---O⁻] species and the reversibility of surface bound superoxide radicals mediating the processes of photogenerated electrons may be accountable for the high activity of SrTiO₃ in photocatalytic water splitting reaction.