OH radical is one of the reactive oxygen species, and is very oxidative. It can injure the body. Rare earth Ce3+ in cerium nitrate can change over between Ce3+ and Ce4+, and can react with OH radicals. In this study OH radicals were produced by nano-TiO2 which can produce OH radicals after irradiated by ultraviolet radiation. Cerium nitrate was mixed with nano-TiO2, then DMPO was employed to catch OH radicals. The result of electron spin resonance(ESR)shows that the quantity of OH radicals produced by nano-TiO2 mixed with cerium nitrate is much less than that without cerium nitrate, thus approves cerium nitrate can effectively rid OH radicals.