In this paper, Taguchi method was applied to determine the optimum operating conditions for textile wastewater treatment by electrocoagulation (EC) with iron electrodes. The removal efficiency of chemical oxygen demand (COD) and turbidity was considered as the performance parameters. L-9 orthogonal array (OA, three factors in three levels) was selected as the experimental design for three controllable parameters mentioned above. These parameters that mainly affect the EC process were specified as initial pH, current density and electrolysis time. Each parameter was examined at three levels using Taguchi method. Performance analysis was followed by a variance analysis in order to determine the optimum levels and relative magnitude of the effect of parameters. Taguchi's the larger the better performance formula was used. The optimum operating conditions in terms of COD and turbidity were found to be initial pH of 7 and 8, current density of 150A/m(2) and electrolysis time of 20 and 30min. At the optimum conditions, COD and turbidity removal efficiencies were obtained as 42.2 and 99.1%, respectively. Operating costs of EC process for COD and turbidity removals were calculated as 1.52 and 1.73Euro/m(3). Besides, the UV-Vis spectrum was used to detect the changes in textile wastewater quality. In EC process, COD concentration of treated effluent was above the permitted direct discharge limits. So, active carbon was used to increase COD removal efficiency of EC process under the optimum operational conditions. COD and turbidity removal efficiencies in the EC/activated carbon (AC) process by adding 2,000mg/l AC were 67.9 and 99.3%, respectively. Operation cost of EC/AC process is calculated as 1.64Euro/m(3). Besides, the operation costs at different operating conditions were also determined.