Abstract-Treating wastewater by bio-reactors combined with electrolytic cells gets better efficiencies in practices. Beside removal of pollutants by electro-oxidation reactions, organic polymerization is considered as another mechanism contributing to remove pollutants in treating wastewater by electrolysis. Therefore, an investigation of organic polymerization in wastewater by electrolysis is carried out in this paper. The common organic substrates of methanol, ethanol and glycol in water can be polymerized by electrolysis. Polymer precipitation contributes to removing 36.9 % and 86.38 % of COD of pulping wastewater and black liquor, respectively. The results indicate that organic polymerization plays an important role in pollutants reduction in treating wastewater by electrolysis.