Objective:To study the role of RNF123 in regulating protein stability of p27Kip1. Methods: Distribution of cell cycle was detected the by flow cytometer in SKOV3 cells,after treatment with serum starvation and release for synchronization purpose. Western blot was used to test the protein level of p27Kip1 of both sictrl cells and siRNF123 cells. SKOV3 cells were transfected with sictrl and siRNF123,western blot was used to analyze half-life of p27Kip1. Results:After serum deprivation for 48 h,SKOV3 cells were arrested in the G1/G0 phase,then serum releasing stimulated the proliferation of G1/G0 to S phase,and the expression of p27Kip1 was decreased during the progress. Moreover,the level of p27Kip1 was higher in siRNF123 cells than that in sictrl cells. After deceasing p27Kip1 expression,half-life of p27Kip1 was delayed. Conclusion:Our results suggest that down-regulated RNF123 can inhibit the degradation of p27Kip1.