The effect of UV irradiation on bromate (BrO3-) formation is investigated in H2O-Br--Cl2/NH2Cl/ClO2 systems. It is found that partial bromide ion was oxidized to BrO3- by Cl2/UVC. NH3 can inhibit the forming of bromate effectively, and no production of bromate is observed by NH2Cl/UVC. The bromate formation capability of ClO2/UV system is weaker than that of the Cl2/UV. Furthermore, the amount of bromate produced in ClO2/UVC is larger than that in ClO2/UVA. Both the formation of bromate and the decomposition of chlorine dioxide are improved in acidic conditions, whereas alkaline conditions lead to reverse effects.