In extended hepatectomy and liver transplantation, accurate estimation of functional hepatic regeneration is more important than volumetric regeneration. We investigated the usefulness of measuring the functional hepatic volume by 99m-technetium galactosyl-human serum albumin scintigraphy (GSA). Extended hepatectomy was performed in 32 patients. These patients were divided into subgroups with or without chronic hepatitis or cirrhosis. Functional hepatic volume GSA scintigraphy (GSA-LV) and determination of hepatic volume by CT (CT-LV) measurements were performed preoperatively, at 2 and 4 weeks and at 3 and 6 months after surgery. The preoperative GSA-LV values were significantly correlated with the hepatocyte volume and the 15-minute retention rate of indocyanine green (ICGR15). Similarly, the hepatocyte volume correlated well with the CT-LV and ICGR15. However, the CT-LV correlated only with the ICGR15. Recovery of the GSA-LV was delayed, and about 90% of the volumetric and functional regeneration was observed within 6 months after the hepatectomy. In contrast, the CT-LV in patients with normal liver remnants returned to approximately 90% of the initial volume within 1 month after the hepatectomy, whereas patients with injured livers regeneration showed gradual recovery to approximately 80% of the preoperative value by 6 months after hepatectomy. We conclude that measurement of functional hepatic volume using the GSA-LV is useful to evaluate hepatic function based on hepatocyte volume.