Purpose: Establishment of the human liver cell lines which permanently express the HCV proteins is important for the large scale production of viral antigen and analysis of the mechanism of hepatocellular carcinogenesis by HCV. Here, we attempted to establish the human hepatoblastoma cell lines which stably express the HCV core protein and examined the intracellular localization of the core protein. Materials and Methods: The cDNA of HCV core protein and neomycin resistance gene were expressed in HepG2 cells by the SR a promoter and human EF-1 a gene promoter, respectively. The core protein was detected by immunofluorescence assay and western blotting. Results: We obtained several HepG2 cell clones which express HCV core protein stably. In transient expression assay, the core protein was localized in the cytoplasm in about 90%, and localized in the nucleus in about 10% of the core-expressing HepG2 cells. But, in the stably expressing HepG2 cell clones, the core protein was localized only in the cytoplasm. No HepG2 cell containing core protein in the nucleus was found in all of the cells which stably express the core protein. Conclusion: The EF-1 a gene promoter is highly efficient in the colony formation by neomycin resistance gene and is very useful for the isolation of human liver cell clones which express foreign genes stably. HCV core protein is localized in both nuclear and cytoplasm of human liver cell in short term but the cells containing the core protein in nucleus seem to disappear in long terrn culture.