The electrochemical polymerizations and characterization studies were made for the monomers 3,4-ethylenedioxythiophene (EDOT) and 3-methylthiophene (3MT) with respect to Pt, GC and Au electrodes. The electrochemical properties of the corresponding polymers poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3-methylthiophene) (P3MT) were also studied in a monomer free LiClO4-acetonitrile solutions. Various polymerization potentials of the monomers in the mixture at fixed concentrations were used to produce the copolymers. Copolymers were shown to be electrochemically synthesized from the monomers and showed intermediate electrochemical properties between their corresponding homopolymers. The electrocatalytic effect was demonstrated using various redox species. The electrocatalytic effect of poly(EDOT-co-3MT) was also studied on a selected inorganic and organic samples. It was found that poly(EDOT-co-3MT) modified platinum electrode is highly selective and sensitive towards these redox species. The detection limits for this copolymer modified Pt electrode were also determined for these redox species.