To further elucidate the molecular mechanisms underlying the suppression of hepatitis B virus (HBV) expression by the hepatitis C virus (HCV) core protein, five molecular clones of HCV cDNA sequence con-taining the 5’ noncoding (5’NC) and the core regions have been isolated from Chinese HBV- and HCV-coinfected pa-tients. Sequence comparison and phylogenetic analysis showed that the HCV sequence cloned from coinfected individu-als is indistinguishable from that identified in other patients. Cotransfection assay confirmed that the core protein ex-pressed from one of the cloned sequence is capable of suppressing the expression of hepatitis B surface and e antigens (HBsAg and HBeAg, respectively). Deletion mapping revealed that the C-terminal hydrophobic region of the HCV core is necessary for the suppression. Results from reporter assays demonstrated that HCV core protein interacts with the HBV C promoter and enhancer II elements and down-regulates the transcription of HBV as well as other cellular and het To further elucidate the molecular mechanisms underlying the suppression of hepatitis B virus (HBV) expression by the hepatitis C virus (HCV) core protein, five molecular clones of HCV cDNA sequence con-taining the 5 ’noncoding (5’NC) and the core Regions have been isolated from Chinese HBV- and HCV-coinfected pa-tients. Sequence comparison and phylogenetic analysis showed that the HCV sequence cloned from coinfected individu- als is indistinguishable from that identified in other patients. Cotransfection assay confirmed that the core protein ex- pressed from one of the cloned sequences is capable of suppressing the expression of hepatitis B surface and e antigens (HBsAg and HBeAg, respectively). Deletion mapping revealed that the C-terminal hydrophobic region of the HCV core is necessary for the suppression. Results from reporter assays demonstrated that HCV core protein interacts with the HBV C promoter and enhancer II elements and down-regulates the transcription of HBV as well as othe r cellular and het