Hydrogen evolution reaction in 3.5 wt% NaCl (simulated seawater) was investigated using Ni-Fe-C cathode, prepared by cathode electrodeposits method on the matrix of A3 steel. The as-prepared Ni-Fe-C cathode coating materials has reached nanometer grade, what is more, the limit of average grain size was about 4.3 nm. As decreasing of the average coating grain sizes, hydrogen evolution overpotential was not decreasing linearly. There was a boundary average coating grain sizes of about 4.3-6.4 nm. The optimal preparation process of Ni-Fe-C cathode was listed as electroplating current density 200 A/m(2), temperature 30 degrees C, pH 1.5 and 60 min. The hydrogen overpotential was only about 65 mV, which was tested in the 3.5 wt% NaCl of 90 degrees C at pH 12. Crown Copyright (C) 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. All rights reserved.