In this paper, optimum process conditions of electroless Ni-P (EN) coating were identified by Taguchi method to minimize cavitation erosion damage of gray cast iron in seawater. The concentration of complexing agent (lactic acid) and concentration of reducing agent in EN coating process have the greatest influence on cavitation erosion characteristics. The EN coating characteristics for the optimal conditions were analyzed using a scanning electron microscope, an energy dispersive X-ray spectrometer, and X-ray diffraction. The EN coating showed the best cavitation erosion resistance characteristic when the P content was 5.37 wt.%, and it had amorphous-nanocrystalline composite structure. Also, cavitation erosion mechanism was investigated by surface analysis of EN coating after cavitation erosion test. (C) 2018 Elsevier B.V. All rights reserved.