A novel oligosaccharide was purified from garlic (Allium sativum L.) bulbs via hot water extraction, ammonium sulfate precipitation, gel filtration and ion exchange chromatography. The molecular weight of the oligosaccharide was determined to be 1800. A nuclear magnetic resonance (NMR) study showed that ten fructose molecules were connected by beta1-2 linkage to a terminal glucose. The oligosaccharide had cytotoxic activities against human malignant lymphoma cells (U937) and colon adenocarcinoma cells (WiDr) in vitro. Furthermore, this oligosaccharide significantly suppressed the growth of murine colon adenocarcinoma cells (colon 26) in vivo. The oligosaccharide also stimulated interferon-gamma production by human peripheral blood lymphocyte in vitro, indicating that it may activate the immunological pathways and suppress the growth of tumors in vivo.