In the present paper it has been shown that Fermi’s semi-empirical atomic mass-formula is inadequate for the estimation of alpha-disintegration energy in the medium heavy and heavy nuclide-regions. A suitable correction-term has been added to the mass-formula based on Duckworth’s new atomic masses and similar to the one proposed by Stern for heavy elements (A⩾208). It is seen that the calculated alpha-decay energies are in numerical agreement with the observed data except for the magic number nuclei which can be satisfactorily explained on the nuclear shell-structure. But even in the latter case the agreement with the experimental results is better when the correction-term is used.