Sargassum fusiforme (Harv.) Setchel is an ingredient of Chinese herbal medicine that has been applied for thousands of years. This study was set up to evaluate the in vivo and in vitro anti-tumor potential of the polysaccharide (SFPS) from S. fusiforme and the immune response in tumor-bearing mice. SFPS was isolated by hot water extraction and ethanol precipitation. The mice inoculated with A549 cells were orally administrated with SFPS at the doses of 100 and 200 mg/kg body weight for 28 days. The effects on the growth of tumor, serum TNF-alpha level, splenocyte proliferation, production of cytokines from peritoneal macrophages in A549-bearing mice were measured. Meanwhile, the cytotoxicity of SFPS on A549 cell line was also studied. Results showed that SFPS could not only significantly inhibit the growth of A549 lung adenocarcinoma in mice, but also remarkably promote IL-1 and TNF-alpha production from peritoneal macrophages, serum TNF-alpha level, and splenocytes proliferation in A549-bearing mice. The results indicate that SFPS has anti-tumor properties in vivo and in vitro, and improves the immune response in tumor-bearing mice. It could act as anti-tumor agent with immunomodulatory activity. (c) 2011 Elsevier Ltd. All rights reserved.