In this study, a Pb-Sn alloy nanowire of 80 nm in diameter and 50 microm in length is obtained by an anodic aluminum oxide nanomold and vacuum die casting method. The upper and lower ends of the prepared Pb-Sn alloy nanowire array are vapor deposited with 3 microm of copper thin film, which serves as the conductive layer of the gas sensor. Experimental results show that the sensitivities of 3 gas sensors fabricated by 3 different Sn-Pb alloy nanowire arrays, namely Sn70%-Pb 30% wt, Sn63%-Pb 37% wt and Sn50%-Pb 50% wt, for detecting a carbon monoxide concentration of 500 ppm under a working temperature of 250 degrees C, were 17.83%, 14.89% and 14.12% respectively.