A protein-bound polysaccharide fraction (JBP-1) was obtained from the fruiting bodies of Cantharellus cibarius. Its chemical composition was studied by the cooperative usage of multiple chemical and spectral methods and characterized to be a fraction with a molecular weight of 4.8 × 10(5) Da and only composed of glucose. Methylation analysis revealed that the sugar residues in JBP-1 are existing as t-, 1,6-, and 1,3,6-linked Glcp sugar residues. The immunocompetence of the fraction was evaluated with the proliferation assay of mouse splenocytes, and the result revealed that JBP-1 could significantly stimulate the proliferation of mouse splenocytes in a dose-dependent manner, with p < 0.001 at the concentration of 100 μg/ml and 30 μg/ml, p < 0.05 at 10 μg/ml. These results give us a primary scientific evidence to further explore the pharmaceutical function of this mushroom.