Abstract: Trifoliate orange（Poncirus trifoliata L.）is highly resistant to Citrus tristeza virus（CTV），but the underlying mechanism has not yet been known. The transcriptomic patterns in leaves of trifoliate orange trees infected with CTV were compared with those of uninfected trees by using Affymetrix citrus genome microarray analysis. A total of 295 genes were identified to be differentially regulated by more than 2-fold following CTV infection，among which were 216 up-regulated and 79 down-regulated genes. BLAST2GO gene ontology analysis showed that a large number of the genes are related to responses to biotic and abiotic stimuli and stresses. A significant number of the genes were involved in metabolism and regulation of ethylene，jasmonic acid，gibberellins，abscisic acid，auxins，salicylic acid. Some responsive genes encodeeither cell wall proteins or those participating in cell wall formation. These results obtained in this study should provide some important transcriptional clues to understanding the mechanism of CTV resistance of trifoliate orange.

Key words: trifoliate orange, Poncirus trifoliata, Citrus tristeza virus（CTV）, transcriptomic changes, CTV-infection