Immunostimulating polysaccharide (BLE-P-I) was purified from young barley leaf. BLE-P-I was further fractionated into two fractions by endo-xylanase digestion. Arabinoxylan-rich oligosaccharide (BLE-P-I-X2) was released by xylanase catalysis. Macrophage activity was compared between before and after xylanase treatment. BLE-P-I-X2 was identified by diverse analytical method and technique.