A novel burdock fructooligosaccharide (BFO-1) was extracted from fresh burdock roots. In our study, we found that BFO-1 possessed immunoenhancing activity in vitro and in vivo. The proliferation activities of splenocytes were significantly stimulated at a BFO-1 dose of 1000 μg ml⁻¹ (p < 0.05), peritoneal macrophages showed increased activities of phagocytosis and acid phosphatase and increased production of NO at a BFO-1 dose of 1000 μg ml⁻¹ (p < 0.01) in vitro. In normal mice, BFO-1 promoted the activities of peritoneal macrophages at dosages of 250 and 500 mg per kg per day (p < 0.01). Similarly, in immunosuppressed mice, BFO-1 enhanced the activities of peritoneal macrophages at the dosage of 1000 mg per kg per day (p < 0.05). Furthermore, S180 tumor-bearing mice that were pre-administered BFO-1 solution showed improved immunological function and suppressed tumor growth. These data indicate that BFO-1 can improve the functioning of the immune system and has the potential to be developed as a dietary supplement and medicinal food.