The electrolytic polymerization of methyl methacrylate (MMA), styrene and tetrahydrofuran (THF) at the anode was investigated by using (C4H9)4NClO4 and (C4H9)4NPF6 as supporting electrolytes. These polymerization reactions were affected by the supporting electrolyte, monomer, and solvent. In the polymerizations of MMA in bulk and of styrene in solutions of dichloroethane and nitrobenzene, a free-radical and a cationic mechanisms were assumed, respectively.Addition of olefins, such as styrene and isobutene which could be oxidized at the anode, increased the current efficiency in the electrolytic polymerization of THF. Poly-THF produced electrolytically in the presence of diphenylethylene, stilbene, and α-methylstyrene contained several units of these olefins in each polymer chain. Oxidation waves of diphenylethylene and stilbene were observed in THF solution by the oscillopolar-ographic measurement. It is considered that the electron transfer from these olefins to anode preferentially occurred to form carbonium ions, which initiated cationic polymerization of THF.