Tumor cells often employ many ways to restrain type I interferon signaling to evade immune surveillance. However, whether cellular amino acid metabolism regulate this process remains unclear and its effects on antitumor immunity are relatively unexplored. Here, we find that asparagine inhibits IFN-I signaling and promotes immune escape in bladder cancer. Depletion of asparagine synthetase (ASNS) strongly limits in vivo tumor growth in a CD8+ T cell-dependent manner and boosts immunotherapy efficacy. Moreover, clinically approved ASNase synergizes with anti-PD-1 therapy in suppressing tumor growth. Mechanistically, asparagine can directly bind to RIG-I and facilitate CBL-mediated RIG-I degradation, thereby suppressing IFN signaling and antitumor immune responses. Clinically, tumors with higher ASNS expression show decreased responsiveness to ICIs therapy. Together, our findings uncover asparagine as a natural metabolite to modulate RIG-I-mediated IFN-I signaling, providing the basis for developing the combinatorial use of ASNase and anti-PD-1 for bladder cancer.