The mechanism underpinning the Hofmeister order of anions on protein stability and other physical and biological processes has been a mystery since its discovery in 1888. In the present study, we investigated electrostatic and Lifshitz-van der Waals (L-vdW) dispersion (electrodynamic) interactions between Hofmeister salts and four monomeric globular proteins. It is shown that structure-stabilizing salts exerted positive L-vdW pressure, whereas structure-destabilizing salts exerted negative L-vdW pressure on proteins. The relative order of the L-vdW pressure followed the Hofmeister series and it overshadowed the electrostatic pressure at high salt concentrations. The net change in the thermal denaturation temperature (Delta T-d) of proteins in 0.8 M Hofmeister salt solutions followed a linear relationship (r(2) > 0.8) with the net electrodynamic pressure regardless of the physicochemical differ- ences between proteins. This study also revealed that segregation of anions into structure stabilizers and destabilizers depended on the dielectric susceptibility of the anion in the ultraviolet region: ions having absorbtion spectrum in the ultraviolet region (e.g., Cl-, Br-, I-, and SCN-) exerted a negative electrodynamic pressure, whereas those with absorbtion spectrum only in the infrared region, for example, SO42-, exerted a positive electrodynamic pressure. The lack of ultraviolet absorption of SO42- ions was because of quenching of ultraviolet radiation by water at below 170 nm.