AIM: To investigate the effects of dexamethasone(DEX) on the pancreatic endocrine function when steroid diabetes mellitus(SDM) occurred. METHODS: 140 rats were randomly assigned to 4 groups according to the clinic doses of DEX administration, Radioimmunoassay and in situ hybridization were applied to evaluate islet hormone changes in pancreas and blood.RESULTS: Changes in fasting blood glucose(FBG) ?fasting serum insulin(FINS) caused by DEX were dose and time-dependent. Changes in somatostatin(SS)mRNA and protein in islet as well as FINS occurred earlier than that of FBG. CONCLUSION: The super-physiological DEX influenced the expression SS and insulin secretion in islet, which may play an important role in SDM.