The surface tensions of aqueous salt solutions of LiCl, KCl, and CsCl were measured as a function of concentration and temperature. By analyzing the results, the thermodynamic quantities of surface formation such as entropy (Delta s), Helmholtz free energy (Delta f), and energy of surface formation (Delta u) were evaluated. Addition of salts into aqueous solution leads to an increase in Delta f but decreases in Delta s and Delta u. The variations of Delta s, Delta f, and Delta u with the change of salt concentration are almost the same for all alkali metal chlorides in spite of their large difference in hydration force.