Electropolymerization of dimethylaminoethyl methacrylate-methyl chloride (DMAEM-MC) by a new redox initiator system, Sn+2/Sn+4 or Sn+2/EDTA, was studied. The polymer was prepared in a batch reactor using graphite as electrodes. A tentative initiation mechanism is proposed to interpret the experimental results. The factors which affect the average molecular weight of the polymer by electrolysis were obtained. The results indicated that the major factors affecting the molecular weight of the polymer were the pH(i) value and the [Sn+2](i)/[EDTA](i) ratio. Temperature and concentration of monomer were minor factors of electropolymerization. Increasing the pH(i) values of the electrolyte decreases the polymer molecular weight at fixed operating conditions. The optimum [Sn+2](i)/[EDTA](i) ratio for obtaining the highest polymer molecular weight depends mainly on the pH(i) value. In the range of higher pH(i) values (3.25 or higher), the optimum ratio of [Sn+2](i)/[EDTA](i) is about 5.00. However, in the range of lower pH(i) values (2.50 or less), the optimum ratio is 1.00. The results also revealed that increasing the monomer concentration increased the molecular weight.