Plants are considered as one of the best sources of diabetic therapy. Being a reliable and sustainable medicinal hub, this study directs the use of Syzygium mundagam in exploring the antidiabetic property. Streptozotocin-Nicotinamide (STZ-NA) induced diabetic rats were treated with Syzygium mundagam bark methanol extract (SMBM). Based on acute toxicity study, the doses of the extract were fixed as 100 and 200mg/kg. Glibenclamide was used as reference drug. The blood glucose level and body weight of the rats were monitored for 28days. After the treatment, rats were sacrificed and the blood biochemical, serum and histopathological parameters were analysed. The in vivo antioxidant levels in liver and kidney were also estimated. SMBM extract (200mg/kg) could significantly reduce the blood glucose level from 580.60mg/dL to 237.60mg/dL on day 28. An accelerated reduction in body weight was observed in diabetic control rats and inhibited by the extract during the study. The haematological parameters were normal compared to normal rats. The values of serum parameters like triglycerides, high-density lipoprotein (HDL), cholesterol and very low-density lipoprotein (VLDL) were close to the values of normal rats. After the treatment, Superoxide dismutase (SOD), Glutathione (GSH) and Glutathione reductase (GR) levels in liver and kidney were found accountable for their antioxidant properties during diabetic condition. The degree of protection set by SMBM extract was clear enough in the histopathology of liver, kidney and pancreas. The phenolic compounds studied in SMBM can be related to these activities. This study proves the ability of Syzygium mundagam to combat the diabetic condition and provides an insight on hidden properties of plants which can be utilized as novel drugs for existing disease complications.