The biological activity of macrofungal polysaccharides (MFPS) depends on their structural features and is a topic of keen interest for researchers since long time. In this communication, we report a water soluble macrofungal heteropolysaccharide (MFPS1) with a molar weight of ˜145,000 g/mol, obtained through alkali extraction, of the wild mushroom, Marasmiellus palmivorus, with significant immunomodulatory properties. In cancer, after the induction of metastasis, the anticancer immune system becomes unresponsive. By studying cytokine secretion and immune phenotyping, it was observed that MFPS1 reactivated the anticancer immune surveillance system. MFPS1 executed T-cell maturation and activation via M1Φ; and also stimulated natural killer (NK) cell and B-cell population. The entire immune activation pathway corroborates its anticancer activity. The RP-HPLC analysis of hydrolyzed MFPS1 showed arabinose, glucose, galactose and mannose as monosaccharide units. The proposed structure of repeating unit was established from methylation analysis, 1D- and 2D NMR study, HR-MS and MALDI-TOF MS analysis.