The initial electrodeposition behavior of Ni-P alloys on carbon steel has been studied in this paper and was found to be greatly influenced by the morphology of the substrate. Preferred nucleation of Ni-P alloy coatings takes place at the crystal boundaries and the surface of cementite. Preferred nucleation and growth of Ni-P coatings also takes place at pearlite because pearlite contains cementite phase and many crystal boundaries. The coatings exhibit a polycrystalline structure composed of gathering nano-sized grains. With a continued electroplating time prolonged, the grains not only present two-dimensional sideward growth, but also display three-dimensional growth on them to form a new polycrystalline layer. (C) 2004 Elsevier B.V. All rights reserved.