In the present report, cyclin-dependent kinasel (CDK1) siRNA was transfected into cells to silence the CDK1 gene expression and study its role in the cell cycle and cell apoptosis. The siRNA targeting CDK1 gene was chemically synthesized and transfected into Hela cells by lipofectamine 2000. The expression levels of CDK1 gene and protein were examined by real-time quantitative polymerase chain reaction (PCR) and Weste blot, respectively. The cell cycle was analyzed by using DNA content analysis by flow cytometry. Cell apoptosis was detected by the Annexin V/PI method. The morphological changes of transfected cells were examined under the microscopy by Wright-Giemsa stain. CDK1 gene was successfully silenced by its siRNA, and the CDK1 protein expression level was decreased significantly, especially from 48th h to 60th h after transfection. The DNA content analysis showed that transfection of CDK1 siRNA led to cells accumulating in G2/M phase. There was no significant difference in the apoptotic rate between transfected cells and the control cells after transfection of CDK1 siRNA for 48 or 60 h. More double nucleus or multinucleus cells could be seen under the microscopy among the transfected cells. The decreased CDK1 expression by siRNA silencing gave rise to cell cycle arrest in G2/M phase but did not induce apoptosis.