Vascular endothelial growth factor inhibitors and checkpoint inhibitors are effective treatments for solid tumors. These new classes of anti-cancer agents frequently cause kidney-related side effects. Although their anti-cancer effects may be enhanced when used in combination, the severity of their kidney-related side effects is unknown. We herein report the first case of thrombotic microangiopathy and mesangial proliferative glomerulonephritis caused by combined treatment with atezolizumab and bevacizumab in a 74-year-old man with hepatocellular carcinoma. The combination therapy was discontinued and replaced with intravenous methylprednisolone followed by oral prednisolone. Subsequently, the urinary protein excretion levels declined.