The structure and strength properties of vacuum Cu-Mo condensates, the components of which do not form chemical compounds in equilibrium conditions and have no mutual solubility in liquid and solid states, are studied by transmission electron microscopy and X-ray diffractometry. It is found that in the process of condensation of copper and molybdenum vapor mixtures in a vacuum, anomalous solutions of molybdenum in the FCC copper crystal lattice are formed. The regularities of irreversible decomposition of the indicated solid solutions are studied under isothermal annealing at 620 °C for 3 h. It has been established that as a result of the thermal influence, a peak of precipitation hardening arises, which has a two-stage character. The experimental results are explained by the formation of hardening BCC and FCC molybdenum particles in the volume of the copper matrix and a change in the mechanism of their hardening action with increasing annealing time.