AbstractThe photochemical reduction of U(VI) to U(IV) sulfate in the presence of α‐hydroxy iso‐butyric acid, accompanied with the decarboxylation and oxidation of the acid to acetone was observed. The reaction rate was found to be of the fourth order, or of the pseudo first‐order with respect to the U(VI) ion concentration in an excess of the acid by following spectrophotometrically the concentration of U(IV) ion produced. A fourth‐order rate equation has been