The influence of thermal annealing on the magnetic properties of alternate-deposited Co58Mo42 and Co82Mo18 thin films were investigated. The saturation magnetization of Co58Mo42 oscillates with increasing the annealing temperature up to 973 K, which corresponds to the structural evolution of Co from amorphous state to hcp paramagnetic, hcp ferromagnetic, fcc ferromagnetic and intermetallic compound Co7Mo6. The immediate formation of Go-Mo amorphous alloys In alternate deposited films is interpreted from a point of view of thermodynamics End attributed to an in situ interfacial amorphization reaction driven by the extra interfacial free energy together with a utilization of heats of condensation during vapor-to-solid transition.