There is here disclosed a method for removing nitrous oxide (N.sub.2 O), carbon dioxide (CO.sub.2) and dinitrogen difluoride (N.sub.2 F.sub.2) from a nitrogen trifluoride gas. The present invention is directed to a method for purifying a nitrogen trifluoride gas which comprises the steps of thermally treating, at a temperature of 250.degree. to 700.degree. C., a zeolite selected from the group consisting of analcime, clinoptilolite, mordenite, ferrierite, phillipsite, chabazite, erionite and laumotite; forming a packed bed of the treated zeolite; and passing the nitrogen trifluoride gas containing the gaseous impurities at a temperature of -125.degree. to 50.degree. C. through the filler layer.