Objective To research the effects of NO on radiation enteritis and detect what role NO - 3 play in the radiation enteritis. Methods NO - 3 can be specially reduced to NO - 2 by nitric acid reductase and it's content was measured by colorimeter,then according to this content,the NO - 3 content in the intestine tissue was detected .At the same time a comparative studies on the pathologic change of tissue morphology. Results The content of NO in radiation enteritis tissue was obviously higher than the normal intestine tissues. The pathologic change in tissue morphology include the mulosa membranes was thiner than the normal groups . The villus of intestines spithelium cells was shorten ,and glandula epithelium was destroyed with great deal of inflammation cell infiltration. Conclusions The inducement and development of the radiation enteritis was confirm with the NO content in the tissue. Nitric acid reductase have useful value in clinical diagnosis of radiation enteritis .