In this paper, we report a study of the strain and its relaxation of epitaxial CoSi2 grown on Si by molecular beam epitaxy (MBE). The strain is measured by a x-ray rocking curve technique and misfit dislocations are determined by transmission electron microscopy (TEM) as the strain relaxes. Results show that the critical thickness of pseudomorphic growth is about 30 nm for growth temperature of 550 °C although there is still a residual strain remained for the thicker films. No apparent complete relaxation of the strain is obtained. Thermal annealing of CoSi2 films is performed and the results of the strain relaxation are discussed.