A trivalent vector containing genes of Watermelon mosaic virus (WMV) coat protein (CP), and replicase genes of Zucchini yellow mosaic virus (ZYMV) and Cucumber mosaic virus (CMV), was constructed for transformation of watermelon (Citrullus lanatus) plants, mediated by Agrobacterium tumefaciens. The integrated foreign genes were identified in the regenerated progenies by polymerase chain reaction (PCR) and Southern blots. The transformation efficiency was about 1.7‰. Resistance to virus infection was determined by mechanical inoculation in the greenhouse and by field trials. The transgenic watermelon lines showed different phenotypes of susceptible, resistant, immune or recovery from virus infections in the late growth stage. A relatively high level of resistance was shown by T3 plants of the line BH1-7. This result indicates the possibility of creating, by transgenic protocols, new varieties of watermelon resistant to viral infection.