From the analysis of the experimental results (high energy electron scattering, X-ray spectra of μ-mesonic atoms), it is pointed out that the radius of nuclear charge distribution, Rp, is very nearly proportional to the cubic root of the atomic number z1/3, ins tead of the usually accepted relation Rp∝A1/3. Under this assumption, we have modified the semi-empirical mass formula. The Coulomb energy term is now assummed to be of the form 3/5 (z2e2)/ropz1/3).The aagreement of the nuclear binding energies calculated fromthe new fomula with the experimental data is definitely better than that of the old Bethe-Weizsacker formula. Also the mass numbers of the most beta-stable nuclei are very correctly predicated by the new formula.