A novel polysaccharide (PFP1) with an average molecular weight of 2.02 × 10 g/mol was isolated from Passiflora foetida fruits through hot water extraction, ethanol precipitation and column chromatography. The structure of PFP1 was determined by GPC-MALS-RI, IC, FT-IR, GC-MS and NMR. The structural analysis showed that PFP1 was a heteropolysaccharide and composed of mannose (48.83%), galactose (32.46%), glucose (6.21%), arabinose (5.88%), fructose (2.24%), galacturonic acid (2.20%), xylose (1.17%), fucose (0.17%), ribose (0.05%), and glucuronic acid (0.78%), with a backbone structure of →1)-α-D-Manp→1,2)-β-D-Manp-linked 1,2,6)-β-D-Manp residues and side chains consisted of →1)-β-D-Galp, →1,4)-α-D-Manp, →1, 4)-β-D-Glcp, →1,3)-α-D-Galp, →1,6)-β-D-Manp, →1,6)-β-D-Galp, →1,2,3)-β-D-Manp and →1,3,6)-β-D-Galp residues. The results of immune-enhancing assays revealed that PFP1 could obviously promote the production of NO and secretion of cytokines (TNF-α and IL-6) of macrophage RAW264.7. These findings demonstrate that P. foetida fruit polysaccharides can be utilized as a potential immune-enhancing functional food.