Abstract Tumor-initiating cells (TICs) are a subpopulation of chemoresistant tumor cells that have been shown clinically to cause tumor recurrence upon chemotherapy. Identification of T-ICs and their related pathways are therefore priorities for the development of novel therapeutic paradigms. We established chemoresistant hepatocellular carcinoma (HCC) xenograft tumors in immunocompromised mice in which an enriched T-IC population was capable of tumor initiation and self-renewal. Using this model, we found CD24 to be up-regulated in residual chemoresistant tumor tissue when compared with bulk tumor upon cisplatin treatment. The determine whether CD24 is a candidate TIC marker for HCC, cell sorting approach was employed to separate CD24-/CD24+ populations derived from HCC cell lines and clinical samples. CD24+ HCC cells were found to be critical for the maintenance of tumor growth, self-renewal, differentiation, chemoresistance and metastasis of tumors. Using quantitative PCR, CD24 was over-expressed in HCCs when compared with their non-tumor counterparts, and CD24 expression was significantly correlated with poor patients’ survival. Using a lentiviral-based knockdown approach, CD24 was found to be a functional liver T-IC marker that drives tumor initiation and self-renewal. Notably, whether by cell sorting or gene-knockdown approach, it was shown by quantitative PCR that the CD24-enriched population consistently overexpressed Nanog. Upon transfection of Nanog cDNA into CD24-knockdown cells, self-renewal and tumor formation were functionally recovered, suggesting Nanog as the downstream effecter of CD24. By Ingenuity Pathway analysis, ‘acute phase response signaling’ was found to be the most significantly altered upon CD24 knockdown in which phosphorylation of Stat3 at the Tyrosine705 residue is critical. Using Stat3 inhibitor (S3I-201), we found that Nanog promoter and its protein were down-regulated in dose-dependent manner in CD24+ HCC cells. CD24 was found to be a functional liver T-IC marker that drives T-IC genesis through Stat3-mediated Nanog regulation. In conclusion, we identified CD24+ HCC cells within bulky tumor, and they functioned to initiate tumor growth and self-renewal through Stat3-mediated Nanog up-regulation. The identification of novel CD24 signaling pathways provides an attractive therapeutic strategy against this deadly disease. Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2445. doi:10.1158/1538-7445.AM2011-2445