It is of interest to use UV-sulfite based processes to degrade pollutants in wastewater treatment process. In this work, arsenic (As(III)) has been selected as a target pollutant to verify the efficacy of such a hypothesized process. The results showed that As(III) was quickly oxidized by a UV-sulfite system at neutral or alkaline pH and especially at pH 9.5, which can be mainly attributed to the generated oxysulfur radicals. In laser flash photolysis (LFP) experiments (λex = 266 nm), the signals of SO3 •− and eaq − generated by photolysis of sulfite at 266 nm were discerned. Quantum yields for photoionization of HSO3 − (0.01) and SO3 2− (0.06) were also measured. It has been established that eaq − does not react with SO3 2−, but reacts with HSO3 − with a rate constant 8 × 107 M−1s−1.