We have studied the mechanism of plastic deformation and fracture of tungsten-cobalt hard alloys over a broad range of compositions and grain sizes of the carbide phase in different stages of loading by uniaxial compression. We have shown that the behavior of each phase component is due to the cobalt content in the alloy and the tungsten carbide grain size. When the alloys are loaded to the yield stress, microcracks appear in them which are stopped at this stage by the deformed layers of the alloy. Residual strain of the hard alloys under uniaxial compression is the result of at least three deformation processes occurring in the alloys when they are loaded: slip along interphase and intergrain boundaries with the appearance of microcracks at this sites, slip in WC grains, and deformation of the cobalt phase. We conclude that slip in the cobalt phase is one of the basic mechanisms for its deformation when the alloys are loaded by compression.