Polysaccharides serve as promising ingredients for health-beneficial functional foods, while there were no investigations into the structural characterizations and bioactivities of an edible mushroom <i>Cantharellus yunnanensis</i>. In the study, crude polysaccharides from this mushroom were extracted by hot water and isolated by ethanol precipitation. Then, a neutral polysaccharide (named CY-1) was purified from the crude polysaccharide by deproteinization with Sevag reagent, decolorization with a kind of macroporous adsorption resin SP-825, DEAE-52 cellulose column chromatography and dialysis. The physicochemical properties of CY-1 were characterized by UV, IR, SEM, NMR, and HPLC analyses. Structural characterizations revealed that CY-1 is a homogeneous heteropolysaccharide with an average molecular weight of 3.06 × 10<sup>4</sup> Da. CY-1 exhibited a honeycomb structure with an irregular branching shape, and it was composed of mannose, glucose, fucose, xylose, arabinose, galactose, rhamnose, and glucuronic acid, with molar fractions of 54.83%, 25.11%, 10.28% 4.53%, 2.12%, 1.64%, 0.83%, and 0.64%, respectively. <i>In vitro</i> hypoglycemic tests showed that CY-1 had an inhibitory effect on α-glucosidase. In addition, CY-1 of 160 µg/mL promoted glucose consumption in normal HepG2 cells. These results suggested that CY-1 may be a potential hypoglycemic agent.