A coupled expression system for plants wasmerase gene was modified by addition of the coding sequenceof nuclear location signal from SV40 large T antigen. Plantexpression vector pBBT7 was constructed with the modifiedT7 RNA polymerase gene under the control of CaMV35Spromoter. Another expression vector pBTG contained cas-sette of gusA controlled by T7 promoter. The two vectorswere co-transformed into tobacco via the Agrobecte-rium-mediated method. Results of GUS activity indicatedthat the co-transformed plant with pBBT7 and pBTGshowed a high level of GUS activity. The results demon-strated that the coupled expression system of T7 polymeraseand T7 promoter was workable in plants.