Background: Methotrexate (MTX) is an antineoplastic drug that is widely used in the treatment of neoplasms. Patients undergoing MTX therapy have a variety of side effects affecting many important organs. Aim of the work: The aim of the present study was to detect the histological and the immunohistochemical adverse alterations that might occur in the jejunum of the adult albino rats following methotrexate therapy and to determine the possible protective role of vitamin A. Material and Methods: Seventy two adult male albino rats were divided into six equal groups. In all groups the animals were sacrificed 24 hours after the last injection. The jejunal specimens were examined using H& E and Masson's trichrome stains and immunohistochemical examination to study the alkaline phosphatase activity using light microscopy. Morphometric study measuring villous height, crypt depth, number of goblet cells, percentage area of fibrosis and the optical density of alkaline phosphatase activity was done in all groups. Results: The methotrexate treated groups' revealed different changes in the jejunum of rats. Distortion and cystic dilatation of the crypts, cellular shedding and dilated blood vessels were found. Morphometric study showed decreased villus height and goblet cells, increased the crypts depth. Immunohistochemical examination of the jejunal sections of the methotrexate treated groups showed weak reaction of alkaline phosphatase enzyme when compared with that of the control group. Conclusion: It can be concluded that the toxic effect of methotrexate on the jejunum of rats can be partially improved with the concomitant use of vitamin A.