In this study, the edible mycelia ofCordyceps sinensis(Berk.) Sacc. were sequentially extracted by petroleum ether, ethyl acetate, ethanol and ultrasonic water-bath (75 °C), and the water extract was further isolated by Sephadex G-100 to afford a petroleum ether extract (PE), ethyl acetate extract (EAE), ethanol extract (EE), glycoprotein (GP) and a purified polysaccharide (PS). In combination with component analysis, the isolated PS showed D-Glc, D-Man, L-Ara and D-Gal in a molar ratio of 8:90:1:1. The average molecular weight of PS was determined as ˜8.3 × 104. The immunomodulatory potentials of these samples (PE, EAE, EE, GP and PS) at three dose levels on the cellular and humoral immune responses of ICR mice against ovalbumin (OVA) were studied. ICR mice were immunized subcutaneously with 100 μg OVA alone or with 100 μg OVA dissolved in saline containing these samples (100, 200 or 400 μg) on days 1 and 15. Two weeks later (day 28), concanavalin A (Con A)- and OVA-stimulated splenocyte proliferation and OVA-specific antibody in serum were investigated. These samples, except for PS, significantly enhanced the Con A- and OVA-induced splenocyte proliferation in OVA-immunized mice at a suitable dose (p<0.05 orp<0.01). OVA-specific IgG, IgG1 and IgG2b antibody levels in serum were significantly enhanced by these extracts and PS compared with the OVA control group (p<0.05,p<0.01 orp<0.001).