The electrochemical formation of Sm-Ni alloys was investigated in a molten LiCl-KCl-SmCl3 (0.5 mol%) system at 723 K. The cyclic voltammogram for a Mo electrode showed the reduction wave from Sm(III) to Sm(II) at 1.60 V (vs Li+/Li), but no reduction wave from Sm(II) to Sm metal. For a Ni electrode, small cathodic currents were observed at potentials more negative than 0.10 V, which indicated the formation of Sm-Ni alloy. The formation of an SmNi2 phase was confirmed by XRD analysis of a sample prepared at 0.10 V for 72 h. The thickness of the SmNi2 film was estimated to be approximately 100 nm. A much thicker SmNi2 film (similar to 20 mum) was obtained by cathodic galvanostatic electrolysis at 50 mA cm(-2) in a time period as short as 1 h. Since Li metal was codepositing during the electrolysis and the SmNi2 film was rapidly formed, this electrochemical formation method was termed the 'Li codeposition method'. The formed SmNi2 film was changed to other alloy phases by anodic potentiostatic electrolysis. The formation potentials of SmNi5, SmNi3 and SmNi2 were found to be 1.20, 0.65 and 0.29 V, respectively.