OBJECTIVES To study the expression of CD34, CD31, CD14, CD10 and factor VIII on blood island of yolk sac (YS), PAS/aorta-germen-mesonephros (AGM) region and hepatic hematopoietic foci. METHODS Thirty-two cases of 3rd-12th weeks human embryo were obtained by drug abortion. Paraffin embedded sections with H.E staining and immunohistochemistry reaction (SABC) were performed. RESULTS YS blood island of 3rd-4th weeks of gestation was consisted of two types of cells. One was vascular endothelial cells located outside and the other hematopoietic cells inside the blood island. Both the two types of cells were CD10, CD14, CD31 and factor VIII positive. Hematopoietic cells were CD34 negative, and vascular endothelial cells were CD34 positive. On 32nd days of gestation, the hematopoietic cells migrated out of YS. On 4th week of gestation, CD34, CD14, CD10, CD31 and factor VIII positive cells appeared in the aorta, mesonephros and hepatic hematopoietic foci. By the 7th week, the number of positive hematopoietic cells reached the peak. In 11th-12th weeks, most cells in these regions were matured red blood cells and were negative for all the antibodies mentioned above excepting for CD34. During 4th-12th weeks, all endothelial cells in embryo were CD34 positive. CONCLUSIONS The hematopoietic cells and endothelial cells of YS blood island co-expressed CD10, CD14, CD31 and factor VIII. Endothelial cells were CD34 positive but hematopoietic cells were negative in YS blood island. The hematopoietic cells of aorta, mesonephros and hepatic hematopoietic foci expressed CD34, CD10, CD14 and factor VIII from 4th week to 7th week. Anti-CD34 antibody could label endothelial cells of every kinds vessels of embryo from 3rd to 12th weeks.