An in situ spectroelectrochemical study was carried out on the formation of 3-methylthiophene oligomer radical-cations (monomer, dimer, and trimer) and the 3-methylthiophene dihydrocation in the solution bulk during the electrochemical synthesis of a poly-3-methylthiophene coating on a conducting glass electrode. A dependence of the concentration of products formed on the cation radius (Li+ and Na+) and nature of the anion ( and ) of the base electrolyte was established. The conversion of charged components into neutral dimers and tetramers of 3-methylthiophene after termination of the anodic polymerization was shown in accord with reported results on the electrochemical polymerization of thiophenes.