Mushrooms are regarded as one of the well-known foods and biopharmaceutical materials with a great deal of interest. Polysaccharide ${eta}$-glucan is the major component of mushrooms that displays various biological activities such as antidiabetic, anticancer, and antihyperlipidemic effects. In this study, we compared the immunostimulatory potency of polysaccharide fractions, prepared from liquid culture of pine-mushroom Tricholoma matsutake, with a potent immunogen lipopolysaccharide (LPS), and their molecular mechanisms on the functional activation of macrophages. We found that fraction II (TMF-II) was able to comparably upregulate or highly enhance the phenotypic functions of macrophages such NO production and cytokine (IL-$1{eta}$, IL-6, IL-12, and TNF-${alpha}$) expression, to LPS. TMF-II triggered the phosphorylation of $I{kappa}B{alpha}$, a critical step for NF-${kappa}B$ activation and translocation. Of the upstream signaling enzymes tested, Src and Akt were thought to be the responsible upstream signaling components in induction of NO production, although TMF-II strongly upregulated the phosphorylation of all MAPK pathways. Therefore, our data suggest that T. matsutake-derived ${eta}$-glucan may exert its immunostimulating activities with similar potency to LPS via activation of multiple signaling pathways linked to NF-${kappa}B$ activation.