The study examined the effect of the operating conditions of the UV photo-Fenton process on COD and TOC removal, biodegradability improvement and mineralization of combined chlorpyrifos, cypermethrin and chlorothalonil pesticides in aqueous solution. The optimum operating conditions for treatment of an aqueous solution containing 100 mg/L of chlorpyrifos, 50 mg/L of cypermethrin and 250 mg/L of chlorothalonil were observed to be H2O2/COD molar ratio 2, H2O2/Fe2+ molar ratio 25 and pH 3. Under the optimum operating conditions, complete degradation of the pesticides occurred in 1 min. Biodegradability (BOD5/COD ratio) increased from zero to 0.38 and COD and TOC removal were 78.56 and 63.76, respectively in 60 min. The treatment resulted in release and mineralization of organic carbon and nitrogen from the pesticide molecules as evident from TOC degradation (removal), and decrease in NH3-N from 22 to 3.9 mg/L and increase in NO3-N from 0.7 to 19.3 mg/L in 60 min. The study shows that UV photo-Fenton process is effective in pretreatment of combined chlorpyrifos, cypermethrin and chlorothalonil pesticides aqueous solution for biological treatment.