In this study, immobilizations of enzymes, invertase and glucose oxidase, were achieved in conducting copolymers of N-pyrrolyl terminated polydimethylsiloxane/polypyrrole (PDMS/PPy) matrices via electrochemical polymerization. The kinetic parameters, v(max) (maximum reaction rate) and K-m (substrate affinity), of both free and immobilized enzymes were determined. The effect of supporting electrolytes, p-toluene sulfonic acid and sodium dodecyl sulfate, on enzyme activity and film morphologies was examined. The optimum temperatures and operational stabilities of immobilized enzymes were determined. PDMS/PPy copolymer matrix was found to exhibit significantly enhanced properties compare to pristine polypyrrole in terms of relative enzyme activities, kinetic parameters and operational stabilities. (C) 2003 Published by Elsevier B.V.