The electrodeposition of lathanium on a Pt electrode was investigated in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid. The cyclic voltammetry, chronoamperometry and constant voltage electrolysis techniques were employed. The results of the cyclic voltammogram and the XRD spectrum of deposits after electrolysis under constant voltage have supported a one step electrodeposition mechanism of lanthanum, La3 3e-→La. The results also indicated that the reduction of La3 ion was irreversible. The transfer coefficient and the diffusion coefficient of La3 ion in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid were calculated as 0.0492 and (1.07-1.19)?0-6 cm2/s, respectively.