Diabetes mellitus (DM), or Type 2 diabetes comprises a chronic metabolic condition defined by increased blood glucose levels. presenting substantial global health challenges. Nanomaterials, specifically gold nanoparticles ‘AuNPs', are increasingly investigated for possessing unique properties and biocompatibility in biomedical potential uses. This study explores the rapid and ecofriendly biosynthesis of ‘AuNPs' using aqueous extracts from five Egyptian seaweeds: Ulva linza, Ulva fasciata, Ulva intestinalis, Petalonia fascia, and Corallina officinalis. Gold nanoparticles were efficiently synthesized by heating each seaweed extract at 90℃ for 10 min, with Petalonia fascia (O.F.Müller) Kuntze demonstrating superior efficacy evidenced by a distinct purple color and a surface plasmon resonance peak at 540 nm. Characterization using UV-vis spectroscopy, transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), and X-ray diffraction (XRD) confirmed the synthesis of spherical ‘AuNPs' with an average diameter of 9.02 ± 1.7 nm and crystalline nature. In vitro assays revealed significant inhibition of α-amylase and α-glucosidase enzymes by the ‘AuNPs', with IC50 values, surpassing the positive control, acarbose. These results highlight the potent antidiabetic properties of ‘AuNPs' synthesized using Petalonia fascia extract, suggesting their potential as natural and effective therapeutic agents for managing DM.