Introduction: Diabetes mellitus (DM) is an endocrine disorder characterized by high blood glucose levels. One of the approaches for treating DM is by regulating the postprandial blood glucose via inhibition of α-glucosidase enzymes. Seagrass is known as a plant containing bioactive compounds, especially for therapy antidiabetic. This research aims to evaluate the α-glucosidase inhibition activity of three species seagrasses (Enhalus acoroides, Thalassia hemprichii and Cymodocea rotundata) from the Banten Bay, Indonesia. Methods: The extracts of all parts (root, leaf, and stem) from three seagrasses were prepared with maceration method using 80% ethanol solvents. The α-glucosidase inhibitory activity was conducted by microplate reader at 400 nm using acarbose as a positive control. Furthermore, the kinetics of α-glucosidase inhibition, phytochemical screening, and total phenolics content were evaluated against extract which has the most potential α-glucosidase inhibition. Results: The result showed that the 80% ethanol extracts of Enhalus acoroides (IC50 values 168.15 ± 2.71 μg/mL) had the most potential α-glucosidase inhibitors activity compared with the positive control acarbose, Thalassia hemprichii and Cymodocea rotundata (IC50 values 197.27 ± 3.07 μg/mL, 425.86 ± 5.15 μg/mL and 429.28 ± 8.89 μg/mL). The kinetic type of inhibition against α-glucosidase was noncompetitive inhibition. The phytochemical compounds were phenols, flavonoid, terpenes, and tannin with the total phenolic content was 28.76 ± 2.46 mgGAE/g. Conclusion: Enhalus acoroides has the strongest inhibitor of α-glucosidase and can be further developed for DM therapy agents.