The study examined solar irradiation for enhancement of Fenton treatment of pesticide chlorpyrifos wastewater. Optimization of the process was achieved by employing the central composite design (CCD). Total organic removal (TOC) removal of 89.2 was obtained under the optimized conditions (pH 3, H2O2/COD 2.25 and H2O2/Fe2+ 10 molar ratios and 60 min reaction time). The improvement of biodegradability (BOD5/COD ratio) index from 0 to 0.41 obviously indicated that biological treatment could be applied after pretreatment for complete treatment of the wastewater. The experimental results and model prediction had an error less than 5 owing to the close data obtained. Solar irradiated Fenton treatment is effective for the pretreatment of pesticide chlorpyrifos wastewater before biological treatment maybe applied. © 2016, Springer-Verlag Berlin Heidelberg.