In the nuclear fuel reprocessing plant, dissolver off-gas (DOG) is supposed to include nitrogen oxides (NOX) during the operation. An adsorption process by mineral zeolite has been studied for DOG treatment that follows a dehydration and iodine removal process. According to the results, the characteristics of the mineral zeolite hydrogenated by 1 N HCl are very favorable for this purpose. As for the actual operation, a small fraction of iodine is supposed to penetrate the I2 removal process to the NOX adsorption process. No degradation has been observed for the NOX adsorption of mineral zeolite by the presence of I2.