In recent years, the utilization of bioactive compounds derived from plant materials and agricultural by-products has attracted increasing attention as a sustainable approach for developing functional and therapeutic agents. Food waste, particularly fruits and vegetables, constitutes a considerable portion of agricultural resource losses. Parts such as eggplant peel and calyx are commonly discarded, although they can serve as valuable sources of bioactive constituents. In this study, extracts of fresh purple eggplant calyx were prepared using a combined extraction technique involving ultrasonic waves and two solvents (absolute ethanol and ethanol–water 50%). The α-amylase inhibitory activity, as a key indicator of blood glucose regulation, was evaluated, and the chemical composition of the extracts was identified using liquid chromatography–mass spectrometry (LC–MS) and gas chromatography–mass spectrometry (GC–MS). The results showed that the eggplant calyx extract was rich in phenolic and flavonoid compounds and exhibited notable enzyme inhibitory potential (64.8% for hydroalcoholic extract and 39.7% for ethanolic extract). The extraction yield of the hydroalcoholic extract (24.9%) was significantly higher than that of the ethanolic extract (3.67%), attributed to the balanced polarity of the water–ethanol mixture. These findings indicate that eggplant calyx, as a low-cost and readily available plant waste, can be considered a natural and economical source for developing bioactive compounds with potential antidiabetic effects applicable in food and pharmaceutical industries. It is noteworthy that, although the antidiabetic properties of eggplant calyx have been mentioned in traditional medicine texts, no experimental or laboratory