Polypyrrole is one of the most important conductive polymers, and has been extensively investigated for potential application, in batteries, solar cells and electronic devices. Although a large volume of research has been conducted on polypyrrole, the nucleation and growth mechanisms of electropolymerized polypyrrole still are not completely understood. In this study, the nucleation and growth mechanisms of polypyrrole coated on a 316L stainless steel surface were investigated using current-time transient measurements together with optical microscopy and atomic force microscopy. It was found that the nucleation and growth behavior of polypyrrole on SS316L could be divided into three stages. The first stage is the incubation period. The second stage is a combination of instantaneous nucleation and 2-dimensional growth and instantaneous nucleation and 3-dimensional growth. The third stage is a combination of instantaneous nucleation and 3-dimensional growth and progressive nucleation and 3-dimensional growth. Different surface morphologies are produced at different coating potentials. The peak current time, and the width of the peak current density, decreased at higher potentials because of severe oxidation of the polypyrrole. (C) 2008 Elsevier B.V. All rights reserved.