Silibinin is a flavonoid extract isolated from milk thistle and has been proved to be a promising chemotherapeutic drug for cancer. However, most of those studies were performed on the human cancer cells, where the effects of silibinin could only be observed on an animal model with a deficient immune system. RenCa cells were isolated from a murine spontaneous renal cell carcinoma, which resembles many features of human renal cell carcinoma, and have been used to establish animal models with a sound immune response. Herein, we investigated the anti-cancer effects of silibinin on RenCa cells, revealing that it inhibited cell viability in both dose- and time-dependent manners. Silibinin slightly triggered apoptosis and significantly induced G2-M cell cycle arrest by downregulating cyclin B1 and CDK1 and increasing expression of p21. Furthermore, silibinin significantly inhibited the growth of RenCa cell xenografts in vivo. In addition, we found that silibinin reduced programmed cell death 1 ligand 1 expression of RenCa cells in vivo and in vitro. Our findings demonstrate that silibinin can inhibit the growth of mouse tumor cells in an animal model with an intact immune system, and silibinin may decrease the immunosuppression effect of tumor cells. Our results provide new evidence for evaluation of Silibinin application in cancer therapy.