The study of EPR spectrum of the Co 2+ ion replacing Zn 2+ in crystals Zn (BF 4 ) 2 × 6H 2 O in a wide temperature area in the X and Q ranges is carried out. The temperature dependence of the line width is measured. The separated spin − phonon contribution to the line width allowed to determine the temperature dependence of the spin − lattice relaxation rate and to show that the main relaxation process is the Raman one. For the first time the temperature dependence of the g-factor for an ion of the iron group is found out.