In the present work, effect of coexisting anions on the degradation performance of UV/chlorine (UV/Cl) processes as an advanced oxidation treatment for the dye containing wastewater was investigated. The results showed that by increasing pH of the solution from 3 to 11, degradation efficiency of UV/Cl process was reduced from 96.2 ± 1.4% to 62.9 ± 3.1%. In the case of 100 mg/L of DR83:1, the removal efficiency was improved from 30.2 ± 1.5% to 93.3 ± 4.7% when the chlorine dose was increased from 100 to 1000 μM. The HCO₃- and Br ions were the main inhibitor and promotor anions responsible for the degradation of DR83:1. The relative contribution of Cl was higher than that for HO and UV, which was about three-times higher than that for HO. The lowest and highest amounts of trihalomethanes were generated at acidic and alkaline conditions as well as low disinfection by products at low pH due to the generation of more HO radicals at acidic pH in comparison to higher pH such that less intermediates were remained to react with chlorine.