An analysis of the reaction and diffusion within polymer modified ultramicroelectrodes is presented This analysis contains a non-linear term related to Michaelis-Menten kinetics In this paper we obtain approximate analytical solutions for the non-linear equations that describe diffusion and the reaction within the polymer-modified ultramicroelectrode by employing the Homotopy perturbation method (HPM) Approximate analytical expressions for substrate and mediator concentration have been derived for all values of parameter gamma(s), gamma(E), and m The obtained analytical results are compared with the available limiting case results and are found to be in good agreement (C) 2010 Elsevier B V All rights reserved