The stability of 16 kinds of metallofullerenes (9 elements) was investigated against the recoil phenomena associated with the capture of neutrons by the metal atoms inside the carbon cages. The yields of the unaffected species were obtained by use of the HPLC separation method and radioactivity measurements. Recoil energy distributions of the metal atoms were calculated theoretically and the effective energy required for destruction of metallofullerenes from inside by recoiling atoms was estimated to be about 10 to 15 eV for the metallofullerenes containing lanthanide atoms.