The purpose of this research was to isolate an active component on immunoytes from 70% MeOH extract of Codonopsis lanceolatae Radix(CLE). CLE was fractionated successively with hexane, methylene chloride, n-butyl alcohol and water, and then the water fraction was separated with molecularporous membrane tubing(m.w. 3,500). Each fraction(50mg/kg) was administered p.o. once a day for 7 days in BALB/c mice respectively. None of these fractions affected the apoptosis and mitochondrial transmembrane potential in thymocyte. Hexane and methylene chloride fractions decreased CD4$^{[-10]}$ CD8$^{+}$ single-positive cells, and the water fraction enhanced CD4$^{+}$ CD8$^{[-10]}$ single-positive cells in thymocyte. The proliferation of thymocytes was decreased by the fraction hexane, but was enhanced by the water fraction. Hexane, methylene chloride and butyl alcohol fractions suppressed the production of nitric oxide, which was not affected by the water fraction. Hexane and butyl alcohol fraction suppressed the phagocytic activity, but water fraction enhanced it. The components(m.w. 3,500 above) separated from the water fraction enhanced the proliferation of thymocyte, the population of CD4$^{+}$ CDB$^{[-10]}$ single-positive cells, and phagocytic activity in macrophage. These results suggest that the stimulative components of proliferation, TH population and phagorytc activity is in the water fraction, and the molecular weight is 3,500 above. (Korean J Nutrition 31(6) : 1076~1081, 1998) 1998)