Objective To investigate the expression of endometrial developingrelated genes, the endometriumlike structure and cells during spontaneous differentiation of hESCs. Methods （1) Embryoid bodies were cultured in suspension for 14 days, fixed in 10% neutralbuffered formalin and embedded in paraffin. Estrogen receptor (ER) was detected by immunocytochemical staining. (2) hESCs were cultured in a 35 mm plastic dish and differentiated spontaneously for 10 days. The expression of ER and Vimentin/Keratin was detected by double immunofluorescence histochemistry. (3) hESCs were cultured in a 35 mm plastic dish and differentiated for 5 days. The expressions of endometrial developingrelated genes including Wnt4, Wnt7a, Wnt5a, Hoxa10, Hoxa11 and ER were detected by RT-PCR. Results (1) The endometriumlike structures were detected in 14dayold EBs and some were positive for ER staining. (2) Some spontaneously differentiated cells from hESCs for 10 days were positive for ER together with Vimentin/Keratin. (3)Wnt7a, Wnt4, Hoxa10, Hoxa11 and ER were detected by RT-PCR in hESCs which were differentiated spontaneously for 5 days.Conclusion During the spontaneous differentiation of hESCs, some cells are liable to differentiate into endometrial stem cells and endomet