He, Ne and Ar are intercalated in a lattice of C-60 under the conditions of ambient temperature and pressure. The mass-analyzed thermal desorption reveals that rare gases are desorbed above 400 K and their desorption amounts are not in impurity level but in stoichiometric level. X-Ray photoelectron spectra in the C1s and valence band regions show different peak profiles. These results indicate that He, Ne and Ar atoms in a C-60 lattice are in the bonding state.