An analysis of reaction and diffusion within an electroactive polymer film deposited on an inlaid microdisc electrode is presented. The theoretical analysis of the steady-state amperometric response for a conducting polymer-modified ultramicroelectrodes is re-studied. The coupled processes of chemical reaction, substrate and mediator diffusion are examined. Simple analytical expressions for substrate and mediator concentrations for all values of reaction/diffusion parameters are presented. The variation of current in terms of m (which defines the ratio of the radius of the inlaid microdisc to the thickness of the polymer layer) is also discussed. The model is based on non-stationary system of coupled reaction/diffusion equations containing a non-linear term related to Michaelis-Menten kinetics of the enzymatic reactions. He's Homotopy perturbation method is used to give approximate analytical solutions of coupled non-linear reaction diffusion equations. A good agreement with available limiting case results is noticed. (C) 2010 Elsevier B.V. All rights reserved.