Abstract: Objective To study the specific mechanism of NUMB regulate tumor proliferation. Methods A stable cell line by knocking down NUMB in Hela was eatablished and the Western blot and qRT-PCR was applied to confirm the knocking out of NUMB. The effect on tumor proliferation in the absence of NUMB was investigated by observing tumor growth in nude mice.The effect on the cell cycle in the absence of NUMB was detected by flow cytometry and Brdu assay. Finally, differential expression profiles of various cell cycle regulatory proteins was detected by using Western blot analysis. Results Western blot and qRT-PCR results indicated that NUMB was specifically and efficiently knocked down in the Hela stable cell line. Tumor growth experiments demonstrated that NUMB depletion significantly promoted the tumor proliferation. Flow cytometry and Brdu assay indicated that NUMB depletion significantly promoted the G1/S transition and enhanced the cell proliferation. Western blot results demonstrated that Cyclin-E protein level was increased in NUMB depletion cell, whereas expression of P27 protein was decreased. Conclusion NUMB might be involved in cell cycle process by regulating Cyclin-E and P27 protein level and thereby has an effect on tumor proliferation.