Nitrogen and oxygen adsorption properties of Li, Na, K, Mg, Ca, or Sr ion-exchanged LSX zeolite (X zeolite with Si/Al=1.0) were investigated. Adsorption of nitrogen and oxygen tended to increase with an increase in the polarizing power of the ion. However, adsorption on MgLSX was much lower than would be expected from this tendency, because Mg93%LSX structure collapsed during the dehydration at 623 K, and Mg at site II in Mg62%LSX did not function as a strong adsorption site owing to its small ionic radius. LiLSX had the highest effective nitrogen adsorption and separation factor of nitrogen and oxygen at room temperature and atmospheric pressure, so LiLSX is considered for the best adsorbent for oxygen-PSA. The effective nitrogen adsorption and separation factor of NaLSX tended to approach those of LiLSX at lower temperature or higher pressure, and those of CaLSX tended to approach those of LiLSX at higher temperature or lower pressure. It is concluded that the effective nitrogen adsorption and separation factor varied with temperature and pressure owing to the effect of the polarizing power of the ions and the number of main adsorption sites.