A B S T R A C TThe performance of a polymeric membrane in an ultrafiltration system under the chosen optimum conditions was studied. To achieve this, four real produced waters were dealt with. To find the optimum conditions, Taguchi method was applied. Results showed that PAN350 membrane is a potential candidate for industrial applications for three feeds which contained oil and total organic carbon (TOC) less than 1,500 and 300 ppm, respectively. The values of oil/grease, total suspended solids, and turbidity rejections were approximately 100%. Although TOC could not be entirely removed, the removal values for TOC were acceptable in this study. For the fourth feed due to the values of oil and TOC which were more than 1500 and 300 ppm, the permeation flux approached zero after 10 min. In the long-time experiments, membrane permeability was equal to 37, 40, and 10 L m À2 h À1 bar À1 for feed 1, feed 2, and feed 3, respectively. Also, the mean of particles size distribution of permeates decreased from 500 to 0.9 nm for feed 1, from 425 to 1.2 nm for feed 2, and from 1,225 to 1.1 nm for feed 3. Experimental calculations demonstrated that both cake layer formation and pore-blocking mechanism affected the flux decline effectively during the process.