By improving Brust method, we synthesize 1-hexanthiol modified gold-silver alloy nanoparticles with an atomic composition of Ag_0.66Au_0.33. By using the alloy nanoparticles as “building block”, we successfully assemble one-dimensional waveguided alloy photonic crystals through a solution processible method. Under the same conditions, the sensitivity of the biosensor built with the waveguided alloy photonic crystals is 2.5 times that of the similar structure made of pure gold. Gold-silver alloy nanoparticles assembled waveguided metallic photonic crystals exhibits potential application in biosensors due to its low-cost fabrication process and simple testing methods.