The present invention provides ribonucleoside 2',3'-cyclic acetals of structural formula I which are precursors or prodrugs of inhibitors of RNA-dependent RNA viral polymerase. These compounds are precursors of inhibitors of RNA-dependent RNA viral replication and are useful for the treatment of RNA-dependent RNA viral infection. They are particularly useful as precursors or prodrugs of inhibitors of hepatitis C virus (HCV) NS5B polymerase, as precursors or prodrugs of inhibitors of HCV replication, and/or for the treatment of hepatitis C infection. The invention also describes pharmaceutical compositions containing such ribonucleoside 2',3'-cyclic acetals alone or in combination with other agents active against RNA-dependent RNA viral infection, in particular HCV infection. Also disclosed are methods of inhibiting RNA-dependent RNA polymerase, inhibiting RNA-dependent RNA viral replication, and/or treating RNA-dependent RNA viral infection with the ribonucleoside 2',3'-cyclic acetals of the present invention. ##STR00001##