Abstract: Objective 　To investigate the effect of PBK/ TOPK expression during differentiation of K562 leukemia. Methods 　The differentiation of K562 cells was induced by Hydroxyurea ( HU) in different con2 cent rations. The differentiation models were evaluated by the staining of benzidine and Wright2Giemsa and fluorescence activivated cell analyzer ( FCAS) . Western blot was deteced the expression of PBK/ TOPK. Results 　HU can induced elyt roid differentiation of K562 cell line in the concent ration of 400μmol/ L in 4 days. The expression of PBK/ TOPK still unchanged, whereas phosphorylation PBK/ TOPK and phospho2 rylation p38 were increased. Conclusion 　HU can inhibit the proliferation of K562 cells and induce the dif2 ferentiation of K562 cells along the elyt roid, phosphorylation PBK/ TOPK expression play a role in this process by phosphorylation p38.