Right-sided round ligament (RSRL) is a rare congenital anomaly that is strongly associated with a number of intrahepatic vascular anomalies. Here, we report a 77-year-old male case of hepatolithiasis associated with RSRL for which resection was performed using right hemi-hepatectomy (RHH). Intraoperative ultrasonography revealed that the portal branch of segment 4 ramified from the right anterior portal branch, and the patient was diagnosed as having RSRL. To decide the resection line, the portal branch of segment 4 was punctured and stained with indigo carmine under ultrasonographic guidance, clearly demonstrating the demarcation line between the right and left hemiliver. RHH was then carried out successfully without injuring the portal branch of segment 4.