An investigation of wastewater treatment by ultrafiltration (UF) is introduced. In the experiments a UF membrane (UFPHT20-6338) and samples of Behshahr Ind. Co. wastewater as feed were used. The effect of operating conditions such as pressure difference, cross flow velocity, shear stress, temperature, concentration of organic components and pH on permeation flux, flux decline and fouling resistance were studied. The results show that a pressure difference more than 3 bar, high cross flow velocities (depending on economic considerations), a temperature of 30degreesC and a pH of 9 are the best operating conditions. Analysis of the wastewater treated by UF represents 91%, 87%, 100%, 85% and 40% reduction in COD, TOC, TSS, [PO4-3] and [Cl-], respectively. Reduction of the phosphate concentration by UF is very considerable.