Thermoluminescence (TL) and ESR phenomena induced by X-ray irradiation of the mixed samples of K2SO4and alkaline earth metal sulfate (MgSO4or BaSO4) were investigated in terms of the reactivities and the crystallogrpahic properties. A high intensive TL resulted from the diffusion of a small amount of Mg2+into K2SO4crystals. The amount formed of K2Mg2(SO4)3, langbeinite, compound had a maximum at the stoichiometric composition. From the ESR measurements, SO−3radicals were found to be easily formed in the langebeinite by excitation. Both the TL and the ESR phenomena were hardly observed in the K2SO4–BaSO4system due to little diffusion of Ba2+with much larger radius than Mg2+. The results were mainly discussed on the basis of the radii of the component cations in these systems. In addition, the fundamental data as to the application to the ESR dosimetry were obtained.