Background: Interferon-based (IFN-based) therapy is effective in the treatment of advanced hepatocellular carcinoma (HCC). However, the issue of resistance to this therapy remains to be solved. The aim of this study was to identify microRNAs (miRNAs) that govern the sensitivity to IFN-alpha in HCC cells Methods: miRNA microarray analysis using IFN-alpha-resistant clones of PLC/PRF/5 (PLC-Rs) and their parental cells (PLC-P) was conducted. Changes in the anti-cancer effects of IFN-alpha were studied after gain-of-function and loss-of-function of the candidate miRNA. Results: miR-146a expression was significantly higher in PLC-Rs than in PLC-P. miR-146a decreased the sensitivity to IFN-alpha through the suppression of apoptosis. Further experiments showed that miR-146a-related resistance to IFN-alpha was mediated through SMAD4. Conclusions: The results indicated that miR-146a regulated the sensitivity of HCC cells to the cytotoxic effects of IFN-alpha through SMAD4, suggesting that this miRNA could be suitable for prediction of the clinical response and potential therapeutic target in HCC patients on IFN-based therapy. (C) 2011 Elsevier Inc. All rights reserved.