A partially oxidized polypyrrole film with a well-defined interface between the conducting and insulating zones is expected to become uniform when the current is interrupted. In practice, this homogenizing process is observed in conducting polymer batteries when they are charged or discharged instantaneously. This process was analyzed by spectroscopic determination of the concentration distribution of the conducting species in the film which was mounted on a glass plate and was connected to an electrode at the end of the film. The film was partially oxidized by applying an oxidation potential for a short time, and then the current was interrupted by disconnecting the electrode. During the anodic electrolysis, the conducting zone became larger, exhibiting a clear front. The localized conducting zone generated in this way was dispersed into the insulating zone under open-circuit conditions, leading to formation of a homogeneous film. The homogenization rate estimated from the speed of dispersion of the conducting zone was closely related to the concentration of the conducting species near the electrode, The proposed mechanism is that oxidation at the conducting front causes reduction near the electrode via a current flowing in the conducting zone. When the concentration of the conducting species near the electrode decreased to 20%, the homogenization stopped, resulting in a localized non-uniform distribution. This was defined as the limit of electric percolation.