In this work, we have theoretically analyzed the non-steady-state current response witnessed at conducting polymer-modified ultramicroelectrodes when the electrode is operating under batch amperometric conditions. Furthermore, the effect of substrate diffusion in the solution adjacent to the polymer film on both the concentration profiles and current response was examined. Analytical expressions pertaining to substrate concentration, mediator concentration, and current response pertaining to all values of diffusion parameters are presented. In addition, we have employed "reduction of order method" to evaluate the approximate analytical solutions of reaction diffusion equations.