[Problem] To provide a strontium ion-exchanged clinoptilolite having excellent nitrogen-absorbing properties; and a method for producing the strontium ion-exchanged clinoptilolite.[Solution] Synthetic clinoptilolite having a strontium ion at an ion exchange site thereof is useful as a nitrogen adsorbent. The synthetic clinoptilolite can be produced by bringing a solution containing a strontium ion into contact with synthetic clinoptilolite under ambient pressure to cause ion exchange.