The kinetics of the hydrolysis of the lactone canrenone, 3-(3-oxo-17β-hydroxy-4,6-androstadien-17α-yl)propionic acid γ-lactone, and the lactonization of its corresponding canrenoic acid salt, potassium 3-(3-oxo-17β-hydroxy-4,6-androstadien-17α-yl)propionate, were studied by spectrophotometrically analyzing the chloroform-extracted lactone from canrenoic acid solution. The log k-pH profiles in the pH range of 1–12 in various buffer solutions at 25.0, 37.5, 45.0, 60.0, 70.0, and 79.9° show that the kinetics of lactonization include hydrogen-ion attack on the undissociated canrenoic acid molecule and a pH-independent closure of the canrenoate anion. In addition to the hydroxide-ion-catalyzed hydrolysis of the lactone, general base-catalyzed hydrolysis in carbonate buffer solution was observed and attributed to carbonate-dianion attack. The rate constants, equilibrium constants, pKa' values, solubilities, and Arrhenius' parameters were obtained. Maximum concentrations of canrenoic acid salt to maintain elegant pharmaceutical preparations are given as a function of pH.