An experimental investigation was carried out on the influence of some polyhydric additives on the thermal behavior of erythrocyte carbonic anhydrase. The stability of the enzyme was analyzed by thermal unfolding and kinetic experiments. The results obtained showed a stabilizing effect of glycerol and sugars (fructose, glucose, sucrose, and sorbitol) whereas ethylene glycol was found to favor protein unfolding. An analysis of the thermodynamic behavior of the enzyme allowed us to determine the transition temperature and the changes in enthalpy, entropy, and free energy in pure buffer and in the presence of additives. The thermodynamic and kinetic results supported the hypothesis that thermal stabilization of carbonic anhydrase is a consequence of microenvironmental modifications, probably related to preferential exclusion phenomena, which strengthen the macromolecule and presence the biologic activity of the enzyme under thermally adverse conditions.