Primary human hepatocytes (PHHs) are widely used as an in vitro model to evaluate various aspects of human hepatic physiology and pathology. However, PHHs isolated from the human liver have very limited ability for ex vivo expansion in culture. Fah−/−/Rag2−/−/Il2rg−/− (FRG) mice are proven to be an ideal bioincubator for repopulation of PHHs. The human liver chimeric FRG mouse is not only a humanized animal model for disease study and drug screening in vivo, but also a potential source of PHHs for cellular therapy. This chapter describes experimental protocols to generate chimeric FRG mice with humanized liver and to isolate PHHs from human liver chimeric FRG mice. Using these methods, PHHs can be expanded to more than 100-fold for harvesting.