have been frequently used for clinical application in China, and the herb residues of turn out to be a waste of resources. To escape from this, the medicine value of herb residues is mined in this article. We isolated hemicellulose polysaccharide AX-I-3b from herb residues by fractional extraction. Monosaccharide-composition analysis revealed that AX-I-3b consisted of arabinose, xylose, and glucose with a molar ratio of 10.4:79.3:1.1. Methylation, NMR and FT-IR analyses showed that AX-I-3b monosaccharide residue was linked as follows: →2,3,4)-β-d-Xylp-(1→, →4)-β-d-Arap-(1→, →4)-β-d-Glcp-(1→. Then, we found that AX-I-3b exhibited antitumor activity against lung cancer in vitro and vivo through MTT assay and xenograft tumor model. Mechanistically, AX-I-3b induced apoptosis in lung cancer cells and xenograft tumors, which is evidenced by the up-regulation of p53, Bax and cleaved caspase-3, and the down-regulation of Bcl-2. Moreover, AX-I-3b synergistically improved the therapeutic ability of cisplatin in xenograft tumors model. Furthermore, AX-I-3b treatment effectively improved the immune organ index, the percentage of spleen lymphocyte subsets and serum cytokine levels in lung cancer mice, supporting that AX-I-3b showed immunomodulatory activity. In conclusion, our results identified AX-I-3b as an antitumor and immunomodulatory agent, providing a new insight into the reutilization of herb residue.