Abstract: Objective To explore whether estradiol could activate the mitogen-activated protein kinase (MAPK) pathway and its effect on the proliferation of endometrial cancer Ishikawa cells. Methods Endometrial cancer Ishikawa cells were divided into three groups: estradiol (E₂) group, U0126(MAPK inhibitor)+E₂ group and control group. The expression of MEK1/2 and ERK1/2 mRNA were determined by qRT-PCR. The activation states of p-ERK1/2 and p-MEK1/2 protein were analyzed by Western blot. Flow cytometry was used to examine the cell cycle. Colony formation ability was detected by colony formation assay. Transwell assay was used to detect the cell migration. Results E2 significantly increased the expression of MEK1/2 and ERK1/2 mRNA(P=0.025, P=0.002). In the U0126+E₂ group, U0126 significantly inhibited the up-regulation of MEK1/2, ERK1/2 mRNA expression induced by E2(P=0.000, P=0.000). E₂ increased the activation level of p-MEK1/2, p-ERK1/2 protein (P=0.049, P=0.028）. In the U0126+E2 group, U0126 significantly inhibited the up-regulation of p-MEK1/2 and p-ERK1/2 protein activation levels induced by E₂ (P=0.018, P=0.003). Compared with the U0126+E2 group and control group, the cells at G₁ stage were less. the colony forming rate was lower and the cells migration ability was higher in E2 group (P=0.017, P=0.009, P=0.000). Conclusion Estradiol could activate MAPK pathway and promote the development of endometrial cancer cells. However, MEK inhibitor could block and inhibit this effect.