A high concentration of hydrogen peroxide (H₂O₂) or H₂O₂/titanium dioxide (TiO₂) is commonly used as a dental bleaching agent. The mechanism of tooth bleaching is that the reactive oxygen species (ROS), especially hydroxyl radical (HO^⋅), derived from H₂O₂ in the bleaching agent remove the color of teeth due to decomposition of organic substances. It has been reported that oxidative stress induced by ROS such as HO^⋅ could be involved in various oral diseases. Thus, H₂O₂ has been shown to be a risk factor for oral tissue injury during bleaching treatment. However, questions remain about the effects of ROS generated from bleaching treatment in detail. Electron spin resonance (ESR) is recognized as one of the most powerful techniques available for the detection of ROS in tissues and cells. We previously developed an ESR-based technique for the detection of ROS reactions in biological systems. In this study, we confirmed O₂^⋅- generated from a low concentration of H₂O₂ (0.3%) /TiO₂ with irradiation of UV light. It was observed that O₂^⋅- production from H₂O₂ (0.3%) /TiO₂ increased in a time-dependent manner of UV light irradiation. Both the L value and ΔE^*ab value rose in H₂O₂ (0.3%) /TiO₂ with irradiation of UV light. These results suggest that a low concentration H₂O₂/TiO₂ system could be applied more safely due to the formation O₂^⋅- but not HO^⋅ as a risk factor for bleaching. In addition, the ESR technique would be useful for characterizing ROS for dental bleaching agents.