Rhus coriaria (sumac) fruit, Punica granatum (pomegranate) peel and Terminalia catappa (Indian almond) leaves' extracts and their anthocyanin and non-anthocyanin fractions were assessed in vitro for DPPH radical scavenging, FRAP, human salivary amylase and Dipeptidyl Peptidase IV (DPP-IV) inhibitory potentials, as well as for their in vivo antidiabetic effects on High-Sugar High-Fat Diet (HSHFD) + streptozotocin (STZ) induced diabetic rats (8-weeks study), by assessing fasting blood sugar, 1hr- and 2 hr-Oral Glucose Tolerance Tests, serum insulin, Homeostatic Model Assessment (HOMA) analyses, serum creatinine, urea and Blood Urea Nitrogen. All extracts and fractions showed antioxidant (DPPH and FRAP) and enzyme inhibition activities (HAS and DPP-IV) and also suppressed STZ-effects in diabetic mice by increasing Superoxide Dismutase, Glutathione S-Transferase and insulin and decreasing HOMA2-IR, urea and creatinine, with sumac extract showing benefits even when administered prior to STZ. These findings suggest that all tested extracts, particularly sumac, possess significant antioxidant and antidiabetic potential.