Abstract: Objective To investigate the variation of cell adhesion molecules (CAMs) on umbilical cord blood (UCB) hemopoietic cells (HPCs) expanded in vitro and the optimal time for transplantation. Methods Long term culture (LTC) was used to expand the UCB HPCs. The expression of CAMs were determined by flow cytometry. Results CD11b+ cells increased significiantly at the 10th day, and quickly increased to 34.3 96 at the 30th day. CD54+ cells increased greatly at the 5thday, and reached 14.9 96 at the 30th day. CD44+ cells reached higher level at the 20th day,while CD34+ cells reached highest level at the 15th day, then decreased gradually but maintained at a higher level than that at the 5th day. Linear regression analysis showed there were interrelated between the expression of CD54 or CD44 and CD34 + HPCs. Conclusion The expression of CD54 and CD44 on UCB HPCs could play a positive role in the homing of UCB HPCs after its transplantation,the suitable time for transplantation is at the 14th day.