Tobacco mosaic virus (TMV) has the potential to highly express foreign gene.A novel TMV-based in trans expression system was constructed.A TMV mutant TSHc had its coat protein replaced with hepatitis C virus (HCV) core antigen gene.Anotherr TMV mutant TSBD was replicase-defective.Coinfection of the two mutants could cause systemic infection in tobacco plants by in trans complementation of their functions.TSHc could effectively replicate and assemble to viral particles,which were a little longer than that of wild-type TMV.HCV core antigen was expressed in whole tobacco plants.A similar expression level of HCV core antigen was detected on serial passages,which suggested that this viral expression system be stable.