In this paper, a comprehensive review of recent advances in the use of mean spherical approximation (MSA) to the primitive electrolyte model for ionic fluids, the non-primitive electrolyte model for ion–dipole mixtures, the one-Yukawa EOS for neutral fluids, and the two-Yukawa EOS for charged colloid systems is introduced. A reasonable mathematical derivation and theoretical explanation are proposed why the dielectric constant of the vacuum cannot be used in the long-range electrostatic term in some successful EOSs for real electrolyte solutions, although the dipolar solvent is treated as explicit molecule in these theories. All the studies show that the MSA approach is of significance both in theoretical research and practical use.