Blocking TGF-β signaling is critical to enhance antitumor immunity. However, there is still no effective TGF-β signaling inhibitors in clinic. Here, we show that clinical medicine ursodeoxycholic acid (UDCA) phosphorylates TGF-β at T282 site via TGR5-cAMP-PKA axis, leading to the increased binding of TGF-β and CHIP. Then, CHIP ubiquitinates TGF-β at K315 site, initiating p62-dependent autophagy sorting and subsequent TGF-β degradation. By degrading TGF-β, UDCA greatly enhances antitumor immunity through restraining Treg differentiation and activation in tumor-bearing mice. In addition, UDCA synergizes with anti-PD-1 to induce stronger antitumor immunity and tumor-specific immune memory in tumor-bearing mice. Notably, UDCA also reduces TGF-β and Tregs in peripheral blood of healthy volunteers and tumor patients. Therapy combining anti-PD-1 or anti-PD-L1 with UDCA has much better efficacy in tumor patients. Thus, our results uncover a novel mechanism for TGF-β signaling regulation and reveal UDCA as a ready-made TGF-β signaling inhibitor in enhancing antitumor immunity.