Abstract Introduction: The twig of Capparis decidua has been traditionally used as an antidiabetic agent but its medicinal use has not been scientifically proved yet. The present study evaluated the antidiabetic effect and antioxidant activities of aquatic extract of twig of C. decidua on the liver and pancreas of diabetic rats induced by streptozotocin (STZ). Materials and Methods: The effect of Capparis decidua was evaluated by biochemical, histological and Fourier-transform Infrared Spectroscopy (FTIR) studies. All biochemical and biophysical parameters were estimated after 15 days of daily oral administrations of the aqueous extract. Results: Findings showed that oral use of C. decidua extract (250 mg/kg) caused significant reduction in the fasting blood glucose levels in diabetic rats when compared to the control rats. Moreover, the altered level of lipid peroxidation, antioxidant, lipid profiles, liver enzymes, and also structural changes were reversed in STZ-induced diabetic rats which received C. decidua extract. Conclusions: In conclusion, aqueous extract of C. decidua has potent antidiabetic and antioxidant activity.