The localization of Ti at grain boundaries after the phase formation of CoSi 2 on Si(111) from a Co-Ti bilayer is examined. For the chemical analysis at the atomic scale, atom probe tomography (APT) is applied. The structure of grain boundaries is analyzed by high resolution transmission electron microscopy (HR TEM). A polycrystalline CoSi 2 film has been formed after annealing. Inside the grains of CoSi 2 , Ti is determined to be present in low concentration of 0.2 at %. An excess of Ti is measured at the grain boundaries. The Ti excess varies for different grain boundaries. HR TEM shows different distances between defects for varying misorientation. The distances between defects are compared with theoretical misfits at the grain boundaries. A relationship between the Ti excess at grain boundaries determined by APT and the defect densities of grain boundaries analyzed by HRTEM is proposed.