The efficiency of diazinon (as insecticides) and nitrate (related to nitrogen fertilizer) removal from contaminated water is investigated through NF membrane technique. The effects of nitrate concentration (40-160 mg/l), diazinon concentration (10-1000 µg/l) and pH (5-9) on the efficiency of a commercial polyamide nanofilter membrane at a constant pressure of (800 KPa) are investigated. The response surface method (Box-Behenken design) is applied in design of experiment. As the diazinon concentration and pH are enhanced, the contaminant removal efficiency increases from 85% to 90%; while nitrate concentration has an opposite effect (removal efficiency reduces about 10%). The regression models obtained for nitrate and diazinon rejection show good fitting to the experimental results (r-squared equal to 94% and 98%, respectively). The models are able to predict the evolution of diazinon and nitrate as a function of concentration and pH at a constant pressure