Transgenic tobacco (Nicotiana tabacum cv. Xanthi-nc) plants were regenerated after cocultivation of leaf explants with Agrobacterium tumefaciens strain LBA4404 harboring a plasmid that contained the coat protein (CP) gene of cucumber mosaic virus (CMV-As). PCR and Southern blot analyses revealed that the CMV CP gene was successfully introduced into the genomic DNA of the transgenic tobacco plants. Transgenic plants (CP+) expressing CP were obtained and used for screening the virus: virus-resistant, delay of symptom development, and susceptible type. Most of the CP+ transgenic tobacco plants failed to develop symptoms or showed systemic symptom development delayed for 5 to 42 days as compared to those of nontransgenic control plants after challenged with the same virus. However, some CP+ transgenic plants were highly susceptible after inoculation with the virus. Our results suggest that the CP-mediated viral resistance is readily applicable to CMV disease in other crops.