This paper is aimed on studying film smoothening effect of supercritical carbon dioxide emulsion (Sc-CO2-E) on nickel film electroplated using an additive-free Watts bath. Morphology of nickel film electroplated with Sc-CO2-E was found to be similar to that of nickel film prepared from electroless plating. Surface roughness (R-a) of nickel film electroplated with Sc-CO2-E was lower than that of nickel film electroplated through conventional method. A minimum R-a was found for nickel film electroplated through conventional method and Sc-CO2-E when increasing current density from 0.010 to 0.150 A/cm(2). The minimum R-a was 69.8 nm at 0.020 A/cm(2) and 14.0 nm at 0.030 A/cm(2), respectively for conventional and Sc-CO2-E case. After the minimum point, increasing rate of R-a, increased was lower for Sc-CO2-E case: this was because of higher hydrogen solubility in Sc-CO2-E. Grain size of nickel film electroplated with Sc-CO2-E was found to be finer than that of conventional case. (C) 2010 Elsevier Ltd. All rights reserved.