Lanthanum (La) thin film was electrodeposited at room temperature (298 K) using lanthanum nitrate, ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) and cosolvent acetone as the electrolyte. Results show that the reduction from La³⁺ to La⁰ involves the transformation of La³⁺→La²⁺ occurring at around -1.7 V vs. Pt and La²⁺→La⁰ occurring at around -2.1 V vs. Pt. The electrolyte BMIMPF₆ exhibits an electrochemical window from -2.5 V vs. Pt to 1.5 V vs. Pt. The low hygroscopic property of BMIMPF₆ allows La electrodeposition under air atmosphere. The precipitate films were observed by scanning electron microscopy and metallographic microscope, showing a dense texture. Then the films were characterized by energy dispersive spectrometry and X-ray photoelectron spectroscopy, confirming therein a large amount of La. The electrochemical tests of changing voltage scan rate and the concentration of lanthanum nitrate reveal that the reduction of La³⁺ is an irreversible process. The diffusion coefficient of La³⁺ in BMIMPF₆ is calculated as 1.47×10^-9 cm²·s^-1. This research provides a simple approach to obtain La thin film, which can be used for the electrodeposition of other lanthanides thin film.