A series of Pt x Co y (x:y =4, 2, 1, and 0.5) alloy nanoparticles deposited on Vulcan XC-72 carbon was prepared through a chemical reduction method. The structures and morphologies of the as-prepared nanoparticles were characterized by X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy, which revealed the formation of Pt–Co alloys during the co-reduction process. Pt x Co y alloy nanoparticles were applied as catalysts in lithium-air batteries. Through electrochemical testing, we found that the Pt based alloy nanocatalysts significantly increased the specific capacity of lithium-air batteries and the increase of Co content in Pt x Co y alloy nanoparticles further enhanced the catalytic activity. This result illustrated that Pt x Co y alloy nanoparticles could be used as an efficient catalyst material for lithium-air batteries with the feature of much reduced cost, but drastically increased catalytic activity.