The aim of this study was to determine, using murine RAW 264.7 macrophages, the immunomodulatory effect of extracellular β-glucan isolated from Pleurotus eryngii (PEBG) and its sulfated derivative (PEBG-S) on signaling molecules implicated in host innate immunity. β-Glucan was extracted and purified from the mycelial culture using optimal medium concentrations. It was then chemically converted to its sulfated form. Monosaccharide composition of β-glucan was characterized with p-aminobenzoic acid ethyl ester-derivatized sugars through highperformance liquid chromatography analysis. Fourier transform infrared structural analysis showed an S=O bond at 1250 cm-1 and C-S-O binding at 815 cm-1 in PEBG-S. 13C nuclear magnetic resonance analysis showed 1,3-linked α-D-mannopyranosyl and 1,3-β-D-glucopyranosyl in PEBG-S. A concentration-dependent increase of nitric oxide production was noticed in RAW 264.7 cells treated with PEBG-S or PEBG; those treated with PEBG-S showed less cytotoxicity than those treated with PEBG. Cellular levels of tumor necrosis factor-α, interleukin-1β, and interleukin-6 were increased by PEBG and PEBG-S treatment, suggesting that they have immunomodulatory activity. Real-time polymerase chain reaction array revealed that the expression levels of nuclear factor-κB and Toll-like receptor signaling genes in cells were upregulated by PEBG and PEBG-S. Moreover, the expression of the β-glucan receptor dectin-2 was significantly upregulated by PEBG and PEBG-S treatment, reflecting immune activation through the dectin-2-Syk-(CARD9/Bcl-10/MALT1) pathway. Our results suggest that PEBG-S could be used as an effective adjuvant or immune enhancer that can be sustainably produced by recycling the by-product of mycelial culture.