Several wells in Zarch District, Iran, are polluted by nitrate and groundwater is a major drinking water source in the region. The aim of this research was to evaluate the efficiency of nitrate removal by two commercial membranes NF90 and BW30 (both Dow Filmtec) using natural water under different operating conditions. Experimental series were conducted to assess the influence of temperature and pressure on nitrate removal by the membranes. The results indicated that BW30 (reverse osmosis) performs better removing nitrate than NF90 (Nano-filter). With a feed of 200 mg-3-.L-1, only permeate from the BW30 membrane met the required quality standard for drinking purposes (50 mg-3-.L-1). When the feed concentration increased to 250 mg-3-.L-1, both membranes failed to achieve the standard in the permeate. The membranes showed similar nitrate removal behaviour under different applied temperatures and pressures. It was concluded that the BW30 membrane can be used to produce drinking water in the study area with influent concentrations below 200 mg-NO3-.L-1.