The correlation between the superconducting Tc and the atom mass (M) for amorphous superconductors has been studied. It is found that the superconducting Tc is inversely proportional to the cubic root of the atom mass, i.e. Tc∞1/M1/3 for the elements of the same group in which they have the same number of valence electrons. The Tc of crystalline superconductors are discussed too, including the superionductivity of high Tc oxide superconductors.