A novel low molecular weight compound polysaccharide (LMW-CPS) was identified from a specific combination of Chinese herb ingredients. The monosaccharide composition of LMW-CPS was consisted of single arabinose, which had an α-L-furanose configuration with an average molecular weight of 2.06 kDa. NMR spectra and monosaccharide constitution analyses revealed that it had a backbone of →5)-α-L-Araf-(1→ with α-L-Araf-(1→ as the terminal residue. In vitro experiments found that it could lead to apoptosis and inhibit hepatocellular carcinoma cell proliferation by arresting them in the S phase. In vivo experiments showed that it protected immune organs such as the thymus and spleen, enhanced immune cell activities, stimulated cytokine release, augmented the abundance of CD8, CD3, CD4, and CD19 positive lymphocytes, and markedly impeded solid hepatocellular carcinoma progression in mice. Hematoxylin and eosin staining and cell cycle examination also indicated that LMW-CPS arrested hepatocellular carcinoma cells at the S phase to induce apoptosis. These findings indicated its promising potential for the treatment of hepatocellular carcinoma.