Abstract: In this study, an immunostimulating particulate β-glucan was isolated from a hot alkaline extract of the fruiting bodies of Ganoderma lucidum. The optimum conditions of 8 hours treatment time, 1:20 solid-liquid ratio and 55℃ for the alkaline extract process were obtained after investigating by single-factor experiments and Box-Benhnken design in terms of the Ganoderma lucidum particulate β-glucan (GLG) increment, and these conditions resulted in a GLG yield of 8.57%. The experimental protocol was approved by the Medical Laboratory Animal Ethics Committee of Jiangsu Provincial Academy of Chinese Medicine. The result showed that resident macrophages were effectively activated by GLG, such as with the up-regulation of co-stimulatory molecules, the secretion of cytokines and phagocytic uptake. GLG could also promote the proliferation of spleen lymphocytes in mice. In addition, IFN-γ production of spleen CD4⁺T cells and cytotoxic T lymphocyte (CTL) responses were significantly enhanced on GLG orally treatment, which ultimately resulted in significantly decreased tumor burden. Taken together, these data suggest that GLG might act as an immune stimulator to exert antitumor effects.