Disclosed herein are a process for the refinement of nitrogen trifluoride gas and an adsorbent therefor. A nitrogen trifluoride (NF3) gas including carbon tetrafluoride (CF4) as an impurity is permeated into a bed of zeolite 3A, 4A or 5A which undergoes ion exchange and impregnation with alkali earth metal and is thermally treated at 150 to 600.degree. C. for 0.5 to 100 hours so as to be able to selectively adsorb nitrogen trifluoride onto the bed, followed by the desorption of the nitrogen trifluoride therefrom.