Template free electrochemical synthesis of crystalline polyaniline (PANI) nanopetals on copper and nanocrystals on zinc substrates has been carried out under optimized experimental conditions. The physico-chemical characterization of the as-deposited PANI nanostructures performed using Scanning Electron Microscope, Transmission Electron Microscope, X-ray Diffractometer, Ultra violet visible spectrometer and Fourier Transform Infrared Spectrometer, reveals formation of crystalline phase of conducting PANI nanopetals and nanocrystals on copper and zinc substrates, respectively. The effect of substrate on the growth and resultant morphologies of the PANI nanostructures has been exemplified with a plausible growth mechanism. The field electron emission studies show that the PANI nanocrystals have better emission characteristics than that of nanopetals. The observed values of turn on and threshold field are found to be comparable with the reported literature. (C) 2013 The Electrochemical Society. All rights reserved.