In recent years, the mechanism of cryogenic treatment to improve the mechanical properties of materials has become a subject of interest. Different mechanism theories have been put forward on this subject. In this study, the effect of shallow and deep cryogenic treatment on the microstructural and crystal structure of tungsten carbide (WC-Co) cutting tool material is investigated with the treatment mechanism being explained. As a result, the shallow and deep cryogenic treatment of WC-Co material did not cause any change in microstructure after high-resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM) investigations. However, the binder Co element in its structure was determined to have martensitic transformation (alpha-Co (fcc) to epsilon-Co (hcp)) by the X-ray diffraction (XRD) method. It was determined in a Rietveld analysis that the epsilon-Co ratio is higher in deep cryogenic treatment than in shallow cryogenic treatment and the untreated sample. In addition, it was determined that tempering after the cryogenic treatment decreases the amount of martensitic transformation.