Objective:To investigate the effect of S-phase kinase-associated protein 2 (SKP2) expression level on radiosensitivity of human hepatocellular carcinoma (HCC) cells and the correlation of SKP2 expression with clinical prognosis of patients with HCC.Methods:The expression levels of SKP2 gene in liver cancer tissues and normal tissues were validated and its correlation with clinical prognosis of HCC patients was analyzed based on the TCGA database. Western blot was used to determine the SKP2 protein levels in HCC cell lines before and after radiation. CRISPR/Cas9 technology was employed to delete the promoter and first exon of SKP2 gene in PLC/PRF/5 (PLC) and Hep3B HCC cells for generating the SKP2 knockout cell lines. The difference of radiosensitivity and cell survival rate between normal (SKP2 +/ +) and SKP2 knockout (SKP2 -/ -) HCC cells was determined by using cell clonogenic assay and CCK8 kit. Results:Compared with normal tissues, the expression levels of SKP2 gene in HCC were increased based on the results of TCGA database analysis. K-M analysis showed that the HCC patients with high SKP2 expression had relatively poor prognosis. The 5-year overall survival (OS) was 34.6% in high SKP2 expression HCC patients and 50.6% in low SKP2 expression HCC patients, respectively ( HR=2.18, 95% CI=1.46-3.27, P<0.001). In vitro experiment showed that the expression levels of SKP2 were significantly increased after radiation in HCC cells. Simultaneously, deletion of SKP2 significantly increased the radiosensitivity of HCC cells. Conclusion:The expression level of SKP2 gene is increased in HCC patients, and patients with high SKP2 expression have worse prognosis than those with low expression. Radiation can upregulate the SKP2 expression levels in HCC cells, while the radiosensitivity of the cells is significantly increased after SKP2 deletion.