Background: Liver regeneration is dependent on the proliferation of hepatocytes. Hepatic progenitorcells are intra-hepatic precursor cells capable of differentiating into hepatocytes or biliary cells.Although liver progenitor cell proliferation during the regenerative process has been observed in animalmodels of severe liver injury, it has never been observed in vivo in humans because it is unethicalto take multiple biopsy specimens for the purpose of studying the proliferation of liver progenitorcells and the roles they play in liver regeneration. Associating liver partition and portal vein ligationfor staged hepatectomy (ALPPS) is a staged procedure for inducing remnant liver hypertrophy sothat major hepatectomy can be performed safely. This staged procedure allows for liver biopsyspecimens to be taken before and after the liver begins to regenerate. Case presentation: The liverprogenitor cell proliferation is observed in a patient undergoing ALPPS for a metastatic hepatictumour. Liver biopsy is acquired before and after ALPPS for the calculation of average number ofliver progenitor cell under high magnification examination by stain of immunomarkers. This is thefirst in vivo evidence of growing liver progenitor cells demonstrated in a regenerating human liver.