Strongly acidic wastewater (H2SO4) with a high arsenic concentration is produced by many industries. The removal of arsenic by traditional sulfide (e.g., Na2S, FeS) from strongly acidic wastewater introduces cations (Na+ and Fe2+) to the solution, which may prevent the recycle of acid. In this study, a new sulfuration agent, phosphorus pentasulfide (P2S5) was employed, and its feasibility in arsenic removal from strongly acidic wastewater was investigated. In the dark, As(III) was efficiently removed, but the removal rate of As(V) was rather slow, which was the crucial defect for this method. We found that this defect can be efficiently overcome by UV irradiation through accelerating the formation and transformation of an intermediate species, monothioarsenate (H3AsO3S) in the As(V) removal process. In addition, the hydrolysis of P2S5 was enhanced under UV irradiation, which resulted in the increase of the arsenic removal efficiencies. Besides, the aggregation of the formed particles was also promoted. Different from FeS and Na2S, P2S5 introduces H3PO4 instead of cations to the solution, which can facilitate the recycle and reuse of arsenic and acid in strongly acidic wastewater.