In this study the effect of crystallite size reduction and microstructure on the electrochemical corrosion behavior of nanocrystalline nickel (NC Ni) were investigated using Tafel polarization and electrochemical impedance spectroscopy (EIS) measurements in 10 wt.% NaOH. NC Ni coatings were produced by direct current electrodeposition using chloride baths in presence and absence of saccharin as a grain refining agent. The crystallite size of NC surface coatings was calculated and analyzed by X-ray diffractometry (XRD). Field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM) were used to study coatings microstructure. The chemical composition of NC surfaces was determined using X-ray energy dispersive spectroscopy (EDS). Our results showed Saccharin decreased the crystallite size but increased the grain size. In addition, corrosion resistance of NC Ni in presence of saccharin increased, which is ascribed to the formation of more stable and protective film. The behavior of passive film growth and corrosion were discussed. Manuscript profile