Object To establish an effective system for Agrobacterium mediated genetic transformation of Poncirus trifoliata Raf Methods The explants used for transformation were the epicotyls from P trifoliata; the Agrobacterium tumefaciens strain was EHA101, provided with the vector plasmid pGA482GG; the coat protein gene (CTV cp gene) was introduced into the transformation plasmid The transformation was proved by PCR and histochemical GUS assay Results In trans for mation of P tri foliata, 20 days epicotyls were suitable for transformation Shoot regeneration frequency was high when cocultivation time was 2-3 days The presence of acetosyringone during cocultivation could enhance the efficiency of transformation Histochemical GUS assay showed that 70 0% of the resistant plants were GUS positive Extra gene was proved to be transformed into P trifoliata plant by PCR analysis Conclusion An effective genetic transformation system has been established for P trifoliata This system will be useful for resistant breeding of P trifoliata