Amorphous WTi alloys were successfully prepared by DC magnetron sputtering in a wide composition range. The sputter deposited WTi alloys thus prepared were spontaneously passive, and their corrosion rates were lower than tungsten and about two orders of magnitude lower than titanium in 6 M HCl solution open to air at 30 °C. XPS analysis showed that tungsten was enriched in both the passive films and underlying alloy surfaces in 6 M HCl solution. The passive films on the WTi alloys were composed of a double oxyhydroxide of tetravalent tungsten and titanium ions. The formation of the double oxyhydroxide film seems responsible for high corrosion resistance of the alloys in comparison with alloying constituents in 6 M HCl at 30 °C.