Abstract: In this study, we investigated the physicochemical properties and in vitro antioxidant and antidiabetic activities of a green tea dust polysaccharide (GTDP). GTDP was extracted from green tea dust using hot water extraction followed by alcohol precipitation. Its physicochemical characteristics, including chemical composition, rheological properties, thermal stability, and microstructure, were analyzed. The in vitro antioxidant and antidiabetic activities of GTDP were evaluated using ferric reducing antioxidant power (FRAP), 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging ability, ferrous ion chelating ability (FIC), and glycosylation and α-glucosidase inhibition assays. The results showed that the GTDP yield was 6.50%, with sugar, uronic acid, protein, and total phenolic contents of 44.73%, 22.58%, 2.92%, and 4.35%, respectively. GTDP contained three polysaccharide fractions with different molecular weights, of which the major component had a relative molecular weight of 88.88 kDa. Monosaccharide composition analysis revealed that GTDP was composed of glucose, arabinose, galactose, rhamnose, galacturonic acid, mannose, glucuronic acid, and xylose in a molar ratio of 31.59:27.11:22.73:8.26:6.29:1.91:1.24:0.87. GTDP exhibited an irregular flake-like structure, characteristic polysaccharide absorption bands, and good thermal stability. Its solution demonstrated shear-thinning, pseudoplastic, non-Newtonian fluid behavior with weak gel-like viscoelasticity. The semi-inhibitory concentration (IC50) values of GTDP in the DPPH, FRAP, and FIC assays were 90.85, 473.37, and 1,159.68 mg/L, respectively. Moreover, the IC50 value of GTDP against α-glucosidase was 0.42 mg/mL, showing an inhibitory activity approximately 2.21 times higher than that of acarbose. The inhibition rate of GTDP on advanced glycation end products (AGEs) was 56.55% at 1 mg/mL, which was approximately 63% higher than that of aminoguanidine. These findings provide a theoretical basis for the comprehensive utilization of green tea dust and highlight the potential of GTDP as a natural antioxidant and antidiabetic agent for functional food and pharmaceutical applications.