Gastrointestinal pathology in diabetic patients has become a source of concern in recent times. The aim of this study was to investigate the ultrastructural and immunohistochemical effects of aqueous leaf extract of Xylopia aethiopica on the stomach in streptozotocin-induced diabetic rats. This study was conducted using thirty adult Wistar rats. The animals were divided into three groups (n=10). Group A was the control animals (administered with equivalent volume of citrate buffer), group B was diabetic animals induced by a single intraperitoneal injection of streptozotocin dissolved in citrate buffer (65 mg/kg) and group C was diabetic animals treated with 200 mg/kg body weight of aqueous leave extract of X. aethiopica for twenty five days. At the expiration of the study, all the animals in each of the groups were sacrificed and the stomach excised and fixed in both 10 % formol and karnovsky fixatives immunohistochemical, light microscopic and electron microscopic studies respectively. The results showed a gradual decline (P<0.05) in the blood glucose level in the extract treated group as against the increment in untreated diabetic group. There was a distortion of the glandular mucosa and epithelium in the untreated diabetic group vis-a-vis the extract treated and control groups. The immunohistochemical staining and percentage immunoreactivity of the stomach of untreated diabetic group showed that the immunoexpression of H+/K+-ATPase were sparse and significantly (p<0.000) lower compared with the control group. There was a better staining pattern for H+/K+-ATPase gastric proton pump in the group treated with aqueous leaf extract of X. aethiopica as compared with the untreated diabetic group. The ultrastructural studies of untreated diabetic group revealed a reduction in the density of mitochondria as compared with the control group. Treatment with leaf extract of X. aethiopica increased the mitochondrial density as well as uniform dispersal of chromatin. It is concluded that diabetes causes gastric pathology thus resulting in morphological changes in the gastric histo-architecture and parietal cells. The aqueous leaf extract of X. aethiopica enhances the recovery/restoration of these defects in streptozotocin induced diabetic rats and as such, may play a significant role in the management of complications associated with diabetes mellitus.