Increased levels of plasminogen activator inhibitor-1 (PAI-1) in tumors have been found to correlate with poor clinical outcomes in patients with cancer. Here, we demonstrate that via the JAK/STAT signaling pathway, PAI-1 induces programmed cell death-ligand 1 (PD-L1) expression in several types of tumor cells and surrounding cells. Blockade of PAI-1 impeded the induction of PD-L1 in tumor cells, resulting in a significant reduction in immunosuppressive cells at the tumor site and an increase in cytotoxic T-cell infiltration, leading to tumor regression. The anti-tumor effect of a PAI-1 inhibitor was abolished in immunodeficient mice, suggesting that PAI-1 blockade induces tumor regression by stimulating the immune system. Combining a PAI-1 inhibitor with an immune checkpoint inhibitor significantly improved tumor regression. Thus, our study reveals that PAI-1 protects tumors from immune surveillance by increasing PD-L1 expression and suggests that therapeutic PAI-1 blockade may prove valuable in treating malignant tumors.