Objective: To investigate the effect of RNA interference silencing of SOX9 (sex determining region Y-box 9) on the proliferation, apoptosis and tumorigenicity of renal cell carcinoma 786-O cells in vitro. Methods SOX9-specific small interfering RNA (small interfering RNA) , siRNA) sequence was the experimental silencing group, and the non-specific siRNA sequence was the control group and were transfected into 786-O cells respectively. The proliferation of 786-O cells was detected by CCK-8 assay and plate clone formation assay, and Hoechst 33342 cell staining was used to detect the proliferation of 786-O cells. Apoptosis of 786-O cells. The effect of RNA interference silencing SOX9 on tumorigenic ability of animals was detected by tumorigenic assay in nude mice. The expression of proliferating antigen Ki-67 protein was detected by immunohistochemistry. Compared with the control group, the OD value of the SOX9 silencing group was significantly lower, and the number of cell colonies was significantly lower than that of the control group, and the difference was statistically significant (P<0.05). Statistical significance (P<0.05). The results of animal tumorigenesis experiments showed that the volume and weight of the tumor in the SOX9 silencing group were significantly lower than those in the control group, and the difference was statistically significant (P<0.05). Immunohistochemical staining showed that the siRNA silencing group The proportion of Ki-67 positive cells was significantly lower than that in the control group, and the difference was statistically significant (P<0.05). Conclusion RNA interference silencing of SOX9 can significantly inhibit the proliferation of renal cell carcinoma 786-O cells, promote their apoptosis, and inhibit renal cell carcinoma 786-O cells. Cancer cell proliferation in nude mice.