Vincristine has been know as antineoplastic,antimitotic drug. pulmonary toxicity is a well-recognized side effect of anticancer therapy.this experimental study was conducted to 40 adult albino rats,which were divided into 2 equal groups.the first group was served as control group with no medications.Each rat from the second group received 1.9 mg/kg vincristine daily I.P. for 4 weeks,then light microscopic study of their lungs was done and revealed alveolar septal edema,interstitial edema,lymphocytic infiltration and pulmonary congestion.while,electron microscopic study showed injury of type I and II pneumocytes, increased collagen fibers and apoptotic changes in alveolar macrophages in the form of fragmentation of nuclei