Abstract: Citrus trees are widely grown in tropical and subtropical climates due to their luscious taste, nutritional and medical benefits. Citrus fruits are native to southeastern Asia and are among the oldest fruit crops domesticated by humans. Breeding programs including the incorporation of genetic resistance to pests and diseases are necessary in this crop. Citrus tristeza virus (CTV) is of particular importance due to its rapid epidemic resulting in severe plant damage. The present research was aimed at transforming Citrus aurantinum with a gene encoding virus coat protein from CTV through Agrobacterium-mediated transformation. P25 coat protein gene was identified and then isolated from different CTV strains. Two regions of the gene were conserved among the genera and subcloned as a single chimer into a pFGC5941 silencing vector. Epicotyls-originated explants of C. aurantium were transformed by EHA105 strain of Agrobacterium tumefaciens. Some of the effective factors in gene transformation were examined by inoculation methods with Agrobacterium such as Acetosyringon effect (0, 50, and 100 �M), inoculation time (5, 10, 15, 20, and 25 min), and co-cultivation period (1, 2, 3 and 4 days). Based on our results, maximum number of transformed plants (13.7%) were obtained under combined treatment of 50 �M acetosyringone after 15 min inoculation time and 2 days of co-cultivation with Agrobacterium. One of the advantages of the current protocol is regeneration of explants through direct organogenesis which avoid callus phase and consequently somaclonal variation.