This is the case of a 77-year-old man with hepatitis C. AFP was increased by 95.9 ng/mL, and abdominal computed tomography(CT)revealed a 20 mm mass in the S6 segment of the liver. Therefore, the patient was referred to our hospital for further examination. Abdominal echo at our hospital showed a 10 mm, low echoic lesion in S6, which tended to shrink. Similarly, CT showed a low-concentration nodule of 10 mm in S6, but the contrast effect in the arterial phase was not clear. EOB-MRI showed a 10 mm nodule of DWI hyperintensity and hepatocyte phase hypointensity in S6. Based on these, a diagnosis of hepatocellular carcinoma(T1N0M0, StageⅠ)was made, and we decided to perform surgery. Intraoperative findings showed no tumor on the liver surface, and echo did not reveal a reproducible nodule. The tumor site was estimated using a 3-dimensional image analysis system created preoperatively. Laparoscopic partial resection of the liver S6 segment was performed at a position distant from the estimated tumor site. Rapid pathological examination showed no malignant findings, but no significant lesion was found in the residual liver, and the surgery was completed. The postoperative pathological diagnosis revealed no clear tumor. EOB-MRI was performed again postoperatively, but no tumor was found in the residual liver. The tumor site that had been indicated preoperatively was resected, and we hypothesized that the hepatocellular carcinoma had spontaneously regressed. Although several mechanisms have been reported for the spontaneous regression of hepatocellular carcinoma, few cases of spontaneous regression during surgery have been reported. We do not have a definite opinion on the treatment protocol for hepatocellular carcinoma that regresses spontaneously; therefore, we will report on past cases.