The synthesis of colloidal AuAg nanoalloys of various compositions has been performed by femtosecond laser irradiation of the aqueous mixture of metallic ions. The mixture of silver-ammonia complex and chloroaurate ions was simply introduced into a glass vial and exposed for several minutes to tightly focused femtosecond laser pulses which induced a strong optical breakdown in the solution and promoted the formation of reactive species to reduce the metallic ions. Homogeneous AuAg nanoalloys have been produced as indicated by the presence of surface plasmon bands that were linearly shifted from 400 to 528 nm with the increase of gold molar fraction in the solution. The result suggested that the atomic gold fraction in the nanoparticles were the same as the gold molar fractions in the solution. Oxidation of Ag nanoparticles possibly caused by oxygen species produced upon the irradiation was not observed.