The basic equations of damage mechanics for commercial-purity molybdenum at 500 and 900 °С has been found experimentally. Plasticity diagram that relate the limiting strain before the failure to the stress state indices has been constructed according to the results obtained by the original device under hydrostatic pressure. Plasticity of the material is found to depend substantially on the type of stress state, which is characterized by the Lode parameter. Plasticity at alternating deformation has been found. The damage theory is used to study the healing of the deformation-induced damage during annealing and to determine the conditions under which irreversible damage, which cannot be healed by heat treatment, appears. The results may be used to develop new technologies of molybdenum deformation treatment.