The drive for miniaturization of electronic devices involves nanotechnology; where single molecules are investigated for the use as electric components.1 Owing to their electronic and magnetic flexibility; endohedral fullerenes have been suggested as one of a possible molecular candidate in future electronics.2 Such molecular components differ from the conventional electronic materials by the degree to which mechanical degrees of freedom affect electrical conductivity.3;4 Understanding of these processes are still in its infancy and in this study in-elastic tunnelling spectroscopy (IETS) which probes the tunnelling current of a single molecule using scanning tunnelling microscopy (STM); with controlled excitation of their vibration modes has been applied to cerium endohedral fullerenes (Ce@C82 and Ce2@C80) to investigate the interplay between electrons and vibrations of these molecules on Cu(111).5 We report here our measured IETS spectrum of single Ce@C82 and Ce2@C80 on Cu (111) and explain the observed IETS peaks by analysing the molecular vibrational spectra simulated using density functional theory calculations.