The anti-programmed cell death-1 protein monoclonal antibody, pembrolizumab is an immune checkpoint inhibitor. While it improves the prognoses of patients with advanced non-small-cell lung cancer, it has been reported to induce various kinds of immune-related adverse events, including hepatotoxicity. Despite the frequency of hepatotoxicity, there is only limited information available regarding the pathophysiology and treatment. We herein report a 48-year-old man with lung adenocarcinoma who was treated with pembrolizumab and developed cholestatic liver injury. In this case, the importance of evaluating the histology of hepatotoxicity and the effectiveness of ursodeoxycholic acid for cholestatic liver injury is indicated.