Dielectric constants for aqueous solutions of L-proline, glyeine, L-alanine, and L-serine were measured from (278.15 to 313.15) K in different molalities up to 0.35 mol center dot kg(-1). Results indicated that the logarithmic values of the dielectric constants for these amino acid-water: solutions increase with increasing molalities of amino acids and conversely decrease as the temperature rises. At given molalities, the relationship of the dielectric constant to the temperature can be expressed by a linear equation for L-proline-water and L-alanine-water solutions and by a quadratic equation for glycine-water and L-serine-water solutions. At given temperatures, dependence of the dielectric constant on the mole fraction can be described by a linear equation for L-proline-water, L-alanine-water, and L-serine-water solutions and by a quadratic equation for glycine-water solutions. An empirical equation is proposed and used to relate log E for the amino acid-water solutions to the temperature and compositions of the solutions.