Treatment of paint manufacturing industry wastewater by electrooxidation (EO) process in which peroxymonosulfate (PMS) and transition metals are added was investigated. In the EO/PMS process, graphite was the cathode while different anode materials (Ti/IrO2, Ti/RuO2, and Ti/SnO2) were used. The anode with the highest chemical oxygen demand (COD) and true color removal efficiency was selected. To determine the catalyst effect on the process, different transition metals (Fe2+, Cu2+, Zn2+) were added and Fe2+ was chosen as the catalyst which provided higher removal efficiency and lower cost. The central composite design was applied for the optimization of the process variables of the EO/PMS/Fe2+ process. Current density, PMS dose, Fe2+ dose, and reaction time were process variables whereas COD and true color removal efficiency were system responses. Under optimum conditions (200 A/m2 current density, 14 mM PMS dose, 2.5 mM Fe2+ dose, 60 min reaction time), the estimated COD and true color removal efficiency by the model were 74.89% and 99.86%, respectively. The experimentally obtained COD and true color removal efficiencies as a result of validation studies were 74.28% and 99.03%, respectively. Quenching experiments showed that hydroxyl and sulfate radicals were both involved in the process.