Objective To explore the relative signal transduction pathway of angelica polysaccharide(APS) inducing K562 cells toward erythroid differentiation. Methods K562 cells were divided into control group and ASP group, the control group cells were routinely cultured and APS group cells were treated with APS(final concentration is 100500mg/L). By using of benzidine staining and spectrophotometry, the characteristics of erythroid differentiation of K562 cell induced by APS were detected; By using of laser confocal microscopy, the distribution of JAK-2 and STAT-5 in K562 cells was observed; By using of Western blotting, the expression of JAK-2 and STAT-5 in nucleus and cytoplasm of K562 cells was detected, By using of imm~uno~pre~cipi~ta~tion, the phosphorylation change of JAK-2 in cytoplasm was tested. Results After being induced by APS, the benzidine staining positive rate of K562 was increased.With increasing the concentration of APS, hemoglobin synthesis in K562 cells was promoted accordingly. After being cultured for 12 hours, 24 hours and 48 hour, the expression of STAT-5 in nucleus of K562 cells induced by APS was significantly higher than that of control group, however, expression of STAT-5 in cytoplasm of K562 cell induced by APS was obviously lower. The expression of JAK-2 in K562 cells was not different between APS group and control group, but the JAK-2 phosphorylation level of APS group was much higher than that of control group.Conclusion APS can induce erythroid differentiation of K562 cells, and the mechanisms may be that APS can promote the phosphorylationthe of J