Diabetes mellitus is a chronic metabolic disorder characterized by sustained hyperglycemia due to impaired insulin secretion, insulin resistance, or both. Enzyme inhibition of α-amylase and α-glucosidase is a proven therapeutic strategy to attenuate postprandial glucose surges. Although synthetic inhibitors such as acarbose are widely used, their gastrointestinal side effects have stimulated interest in natural dietary alternatives. The present study investigates the phytochemical composition and in vitro antidiabetic activity of ethanolic extracts from five rice varieties: Mapillai Samba, Red Rice, Karuppu Kavuni, Karudan Samba, and Ponni Rice. Extracts were prepared using Soxhlet extraction and evaluated for α-amylase and α-glucosidase inhibition across concentrations ranging from 10 to 500 µg/mL, with acarbose serving as the reference inhibitor. Qualitative phytochemical screening revealed that all varieties contained alkaloids and flavonoids, while pigmented rice types exhibited higher diversity of secondary metabolites. In enzyme assays, Karuppu Kavuni showed the strongest inhibitory activity (91.40% for α-amylase and 91.10% for α-glucosidase at 500 µg/mL), closely comparable to acarbose (93.25% and 95.16%, respectively). Red Rice and Mapillai Samba demonstrated moderate activity, whereas Ponni Rice showed the least inhibition. Statistical analysis confirmed significant differences between rice varieties (p < 0.05). These findings suggest that pigmented rice varieties, particularly Karuppu Kavuni, may serve as functional foods or nutraceutical sources for managing postprandial hyperglycemia. Future in vivo validation and phytochemical characterization are warranted.