Transforming growth factor (TGF)-beta induces cell growth arrest in well-differentiated hepatocellular carcinoma (HCC) while hepatitis B virus X protein (HBx) minimizes the tumor suppression of TGF-beta signaling in early chronic hepatitis B. However, how to reverse the oncogenic effect of HBx and sustain the tumor-suppressive action of TGF-beta has yet to he investigated. The present study examined the effect of TGF-beta and a c-Jun N-terminal kinase (JNK) inhibitor on cell growth in HCC cells with forced expression of HBx. It was found that HBx promoted cell growth via activation of the JNK/pSMAD3L pathway and inhibition of the transforming growth factor-beta type I receptor (TPRI)/pSMAD3C pathway. pSMAD3L/SMAD4 and pSMAD3C/SM.AD4 complexes antagonized each other to regulate c-Myc expression. In the absence of HBx, TGF-beta induced cell growth arrest through activation of the T beta RI/pSMAD3C pathway in well-differentiated HCC cells. In the presence of HBx, TGF-beta had no effect on cell growth. JNK inhibitor SP600125 significantly reversed the oncogenic action of HBx and favored TGF-beta to regain the ability to inhibit the cell growth in HBx-expressing well-differentiated HCC cells. in conclusion, targeting JNK signaling favors TGF-beta to block HBx-induced cell growth promotion in well -differentiated HCC cells. As an adjunct to anti-viral therapy, the combination of TGF-beta and inhibition of JNK signaling is a potential therapy for HBV-infected HCC.