INTRODUCTION: Cinnamon zeylanicum (CZ) bark is widely used as supplement for diabetic management, there are concerns about its safety and potential toxicity at high doses, and limited evidence to support its efficacy. To investigate this further, this study examines the effects of Cinnamon zeylanicum aqueous extract (CZAE) on various factors in diabetic rats, including body weight, blood glucose level, biochemical parameters, histological changes, and gene expression. MATERIALS AND METHODS: In the study, 30 male Sprague Dawley rats were divided into five groups of six animals each. Type 2 diabetes mellitus (T2DM) was induced in all groups except the negative control by a single intraperitoneal injection of streptozotocin (STZ). The rats in the intervention groups (Groups C, D, and E) were given CZAE at 1000, 1500, and 2000 mg/kg, dose respectively, for 28 days. The body weight and fasting blood glucose were monitored weekly, and their liver and renal profiles were analyzed. Histology was assessed with hematoxylin and eosin stain, and apoptotic gene expression was examined in liver and renal tissues. RESULTS: The body weight of rats in intervention groups increased compared to the control group. There was a significant decrease (P<0.001) in blood glucose levels. The extract significantly reduced (P<0.05) liver biochemical markers in the intervention groups compared to the control group. The histology of the liver & kidney improved (p<0.001) with upregulated Bcl-2 and down-regulated BAX genes in preventing apoptosis in the intervention groups. CONCLUSIONS: High doses of CZAE are safe and effective for T2DM.