In this paper, the effects of organic acid radicals on degradation of Orange II in UV-Fenton system with hydroxyl-Fe-pillared bentonite as catalyst were studied in detail. The results showed that the rate constants of UV-Fenton reaction will decrease when the system contains sodium citrate or sodium malonate. While the rate of Orange II degradation in UV-Fenton system could increase up to 33.3% and 41.7% when EDTA and sodium oxalate were present, respectively. As the additional TOC of EDTA is higher than sodium oxalate, adding sodium oxalate is a more promising enhanced method for Orange II degradation in UV-Fenton system. The rate of Orange II degradation could increase 25%, 42% and 175% when the concentrations of additional sodium oxalate increased up to 0.1 mM, 0.2 mM and 0.4 mM, respectively.