Huangshui (HS), the by-product of Chinese Baijiu, has attracted considerable attention due to its nutrient and microbial composition; however, none of the studies has explored the polysaccharides in HS yet. Here, from HS, we isolated a novel polysaccharide, HSP-3, with an average molecular weight of 26.40 kDa. The structure was elucidated based on monosaccharide composition and methylation analysis, NMR, FT-IR, and AFM analysis. It is mainly composed of mannose (46.6%), galactose (17.3%), arabinose (11.2%), glucose (10.5%), xylose (8.2%), fucose (5.2%), and rhamnose (1.0%). The backbone of HSP-3 was made up of → 2)-β-d-Manp-(1 → 2,6)-β-d-Manp-(1 → 6)-β-d-Galp-(1 → 3,6)-β-d-Galp-(1 → 4)-α-l-Rhap-(1 → 3,4)-α-l-Rhap-(1 → . Moreover, stimulation of the production of ROS, NO, TNF-α and IL-6, upregulation of the mRNA and protein expression levels of TNF-α and IL-6 in THP-1 cells, and enhanced the pinocytic and phagocytic capacities of THP-1 cells exhibited significant immunomodulatory properties of HSP-3. Altogether, this study suggests that HSP-3 could be used as an active component in functional foods.