In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air-and-water-stable 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate ([emim]OTF) ionic liquids. The electrochemical behaviors of bare and niobium coated 304 stainless steel were evaluated by electrochemical tests in simulated PEMFC environment. The results show that deposited niobium is finely dispersed on the surface of 304 stainless steel as isolated islands and that the height of isolated island is within 100 nm. The result of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD) manifest that the smooth and strong chemical inertness compound film is obtained on the surface of 304 stainless steel, which is mainly composed of NbO and Nb2O5. The thin composite film acts as barrier and remarkably improves the corrosion resistance of 304 stainless steel in PEMFC environment