Novel nano- and microstructures of polypyrrole were synthesized by an electrochemical template-free method on Nickel (Ni) electrode. Scanning Electron Microscope (SEM) study revealed nano- and micro-snails of polypyrrole after the one-step potentiostatic electropolymerization of pyrrole in aqueous alkaline solution. The influence of the anodic polarization time on the morphological, mechanistic and electrochemical characteristics of these novel polymeric films was investigated. An appropriate mathematical model was established and showed that two simultaneous 2D growth instantaneous nucleation processes and a successive 3D growth progressive nucleation mechanism are involved in the polypyrrole micro-snails formation under a diffusion control. Polypyrrole layers generated from these processes appeared to be in different overoxidation states from X-ray Photoelectron analysis and from the electroactivity study of the modified Ni electrode. (C) 2014 Elsevier Ltd. All rights reserved.