Laboratory investigations for one step purification of recombinant human IL-4 (rhIL-4)with cation ion-exchange chromatography are presented.The method is easy to operate and gives no dilution effect on the sample.The purified rhIL-4 is of high purity (≥95%),high biological activity(≥10 MU/mg) and low toxicity(ET≤0.5 ZU/L),which meets the criteria of cytokines for the further experiemental research.Furthermore,purity of rhIL-4 can be increased as high as 98% with higher biological activity when two steps of purification were employed by using combination of ion exchange and gel-filtration chromatographies.