Objective To investigate the expression of maternal embryonic leucine zipper kinase (MELK) in esophageal squamous cell carcinoma and its significance. Methods The surgical resection specimens of 139 patients with esophageal squamous cell carcinoma who were admitted to Peking University Cancer Hospital from August 2009 to July 2013 were selected. MELK expression in esophageal squamous cell cancer tissues was detected by immunohistochemistry. The relationship between MELK expression and clinicopathological characteristics of patients was analyzed. MELK expression in 6 esophageal squamous cell carcinoma cell lines (ECA109, KYSE150, KYSE30, KYSE70, KYSE180 and KYSE510) was tested by Western blot, and the cell line with high MELK expression was selected, and the expression of MELK was knocked down by lentiviral infection. The effect of MELK on tumor cell migration and invasion was examined by Transwell method, and the effect of MELK on cell proliferation was verified by CCK-8 method. Results MELK is highly expressed in 100 cases (71.9％) of esophageal squamous cell carcinoma, and the positive expression rate of MELK in patients with stage T3-T4 was higher than that in patients with stage T1-T2 (χ2=4.702, P= 0.030). The poor differentiation and lymph node metastasis inclined to higher MELK positive expression rate, but the difference was not statistically significant (χ2 = 2.761, P= 0.097; χ2= 0.994, P=0.319). MELK was highly expressed in ECA109 and KYSE150 cells. The Transwell test results showed that the number of migrating cells of EEL109 and KYSE150 cells in the MELK knockdown group was decreased when compared with the negative control group [(77±10) cells vs. (126±8) cells, t=6.56, P<0.05;(37±4) cells vs. (105 ±3) cells, t= 24.27, P< 0.05], and the number of invading cells was decreased [(47 ±7) cells vs. (154±9) cells, t= 17.08, P< 0.05; (37±2) cells vs. (184±4) cells, t= 54.09, P< 0.05]. CCK-8 proliferation studies showed that the proliferation of ECA109 and KYSE150 cells in the MELK knockdown group was inhibited (both P< 0.05). Conclusions The high MELK expression in patients with esophageal squamous cell carcinoma is associated with T stage. High expression of MELK can promote the proliferation and invasion of tumor cells in esophageal squamous cell carcinoma.