Atmospheric-pressure-plasma nitriding of titanium alloy Ti-6Al-4V has been achieved by using a pulsed-arc plasma jet with a N 2 /H 2 gas mixture, where the plasma jet plume is sprayed onto the titanium surface under atmospheric pressure. We successfully formed a titanium nitride layer on the sample surface. Moreover, the diffusion layer was also formed, the hardness of which was increased from that of as-received titanium. The nitride layer growth was found to be diffusion-controlled, as in other conventional nitriding methods.