In this study, one polysaccharide (GFP1), with an average molecular weight of 1.4 × 10(5)Da, was isolated from Ginseng fruits. GFP1 was composed of galactose, glucose, rhamnose, and arabinose in a molar ratio of 6.1:2.0:1.1:3.2, and had a backbone mainly consisting of (1 → 6)-linked-Galp, (1 → 3,6)-linked-Galp and (1 → 3,6)-linked-Glcp residues, which was terminated with terminal (1 →)-linked-Araf or -Rhap attached to O-3 position of (1 → 3,6)-linked-Galp and (1 → 3,6)-linked-Glcp. We also evaluated the effect of GFP1 on anti-tumor immune response in Lewis lung carcinoma (LLC)-bearing mouse model and explored the possible mechanism. GPF1 could significantly inhibit tumor growth and lung metastasis in vivo, increase the relative spleen and thymus weight, promote ConA or LPS-induced spleen lymphocytes proliferation, elevate the activities of NK cell in spleen, and increase the serum concentration of interleukin-2 (IL-2) and interferon-γ (IFN-γ), as well as the ratio of CD4(+)/CD8(+) in LLC-bearing mice. All these findings implied that GFP1 could effectively inhibit tumor growth and lung metastasis via activating immune function and provide insights into the mechanism of GFP1 in the prevention and treatment of lung cancer.