Treatment of pulp and paper mill wastewater using ultrafiltration (UF) membranes was investigated in this study. A Taguchi experimental design was implemented for design of the experiments to investigate optimum operating conditions that achieve higher removal of pollutants and lower membrane fouling. Four factors at three different levels were considered for the experimental design, namely, pH, temperature, transmembrane pressure, and volume reduction factor (VRF). Under the optimized conditions (pH 10, temperature 25 degrees C, transmembrane pressure 6 bar, and VRF 3), a 35% flux decline caused by fouling occurred. Higher rejections were observed for total hardness (83%), sulfate (97%), spectral absorption coefficient (SAC(254)) (95%), and chemical oxygen demand (COD) (89%), but not for conductivity (50%), under these conditions. From the analysis of variance (ANOVA), it was determined that the factor of pH made the greatest contribution to response parameters. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) analyses showed that membrane fouling occurring on the membrane surface and within pores decreased by optimizing the operating conditions. The Taguchi method was successfully applied to find the optimum conditions for the treatment of pulp and paper mill wastewater using the UF process.