Acidic properties of HZSM-5 type zeolites containing alkaline earth metals, which have showed an excellent performance for methanol conversion to light olefins at temperatures above 500°C, were investigated by means of NH₃-TPD, ²⁷Al NMR and FT-IR. It was found that a part of the alkaline earth metals changes the strong acid sites of HZSM-5 to weak ones. It was also found that the release of a part of the alkaline earth metals from the weak acid sites are promoted by steaming, resulting the regeneration of the strong acid sites. The strong acid sites promote the formation of coke deposits, which are responsible for deactivation of the zeolites.The similar release of the alkaline earth metals from the weak acid sites also occurred in the presence of CO₂. It is suggested that the release of the alkaline earth metals is apparently depressed by the presence of large amounts of the alkaline earth metal salts on the outer surfaces of zeolite crystals.