The ubiquitin-proteasome system(UPS), one of the major protein degradation pathways, plays an important role in the regulation of protein turnover. E3 ubiquitin ligases are pivotal for determining the specific substrate that will be modified via ubiquitination. E3 ubiquitin ligase take part in various physiological and pathological process, including cancer development. However, whether E3 ubiquitin ligase RNF216 is involved in the regulation of the tumorigenesis remains to be elucidated. To investigate the underlying mechanism of how RNF216 might contribute to the development of tumor, we established a xenograft tumor model of breast cancer using breast cancer cell EO771 in wild type and RNF216^-/- mice. We found that RNF216^-/- mice had a signifcant reduction of tumor volume and improved survival compared with the wild type mice. Additionally, intraperitoneal injection of CpG could inhibit the growth of tumor in mice. And tumor volume was significantly decreased in RNF216^-/- mice with CpG treatment than wild type mice with the same treatment. Further study demonstrated that CpG stimulation on RNF216^-/- mice promoted Th1 cytokine secretion, including TNF-α, IFN-γ and IL-6, while there was no significant difference in IL-4, a typical Th2 type cytokine. Collectively, our study illustrates that RNF216 contributes to the development of tumor through inhibiting Th1 immune response.