Background:Diabetes mellitus has been shown to cause severe impairment in exocrine pancreatic function and cyto-architecture. Ocimum grattissimum has been reported to lower blood glucose levels in experimental diabetic animals. This study, therefore, aims to investigate if treatment with O. grattissimum can alleviate these pancreatic complications of diabetes mellitus. The phytoconstituents and median lethal dose of the plant extract were determined.Materials and Methods:Eighteen rats were divided into three groups of six rats each. Diabetes mellitus was induced by single intraperitoneal injection of 65 mg/kg streptozotocin. Group 1 was the control and were given normal feed only; Group 2 was of diabetic untreated rats, while Group 3 was O. grattissimum-treated diabetic rats at a dose of 1,500 mg/kg. After 28 days, blood was collected by cardiac puncture of the anaesthetised animals and the serum was obtained for analysis of serum pancreatic amylase. Permanent preparations using routine biopsy method were employed for histological preparations.Results:Results showed that the level of pancreatic serum amylase in the test groups (diabetic and diabetic-treated) were significantly higher (P < 0.05) than the control group, while the diabetic-treated group was significantly lower than the diabetic group. Atrophic acinar tissue without β-cells was noted in the diabetic and diabetic-treated groups. Patchy areas of necrosis, oedematous interstitium, haemorrhagic and necrotic acinar cells were present in diabetic-treated groups.Conclusion:Direct association exists between the hyperglycaemic state caused by diabetes mellitus and the elevation of the serum pancreatic amylase and distortion of pancreatic cyto-achitecture. O. grattissimum-treatment reduced serum pancreatic amylase level to near normal and limit the extent of structural damage.