Ellipsometric analysis of the buried graphitized layer formed in the He + -implanted and annealed diamond has been made. Spectroscopic ellipsometry data in the 360–1050nm range at the incident angles between 65° and 75° were fitted based on a three-layer structure model. Using optical spectroscopy, atomic force and white-light interferometry microscopy data the n and k spectra of graphitized layer, its thickness and roughness were determined with high accuracy.