© 2021 Desalination Publications. All rights reserved.In this study, optimum treatment conditions for paint industry wastewater were determined by response surface methodology (RSM). Wastewater treatment experiments were performed in jar test using the coagulation/flocculation method. FeCl3·6H2 O, Al2 (SO4)3·18H2 O, and FeSO4·7H2 O coagulants were used in the treatment experiments. pH, coagulant dose, and mixing speed were selected as the most important parameters for wastewater treatment and chemical oxygen demand (COD), total suspended solids (TSS), turbidity, and color analyses were examined for each coagulant. After determining the coagulant (FeCl3·6H2 O) which provided the best treatment efficiency, a central composite design (CCD) was applied for optimization of treatment conditions by using RSM. Design Expert 7.0.0. the program was used for the design of treatment experiments and analysis of results. COD, TSS, color, and turbidity values were processed by the program after experiments. 3D graphs and statistical results created by the program were interpreted. The equations obtained using the coefficients in the model created by the program were solved and the optimum values of the independent variables were calculated. Using these values, the lowest pollution values were determined as (mg/L) COD 68.636, color 2.42, turbidity 1.79 NTU, and TSS 10.135. Optimization results from the program were examined and the optimum values of treatment parameters were suggested as pH 7.54, coagulant amount 1,080.49 mg/L, and mixing speed 146.16 rpm. The lowest pollution values under optimum conditions were (mg/L) COD 71.07, color 1.00, turbidity 2.74 NTU, and TSS 7.50. Under optimized conditions COD, TSS, color, and turbidity removal were 94.1%, 95.3%, 97.1%, and 99.5%, respectively.