Abstarct: Citrus canker, decreases performance and quality of citrus produce mainly in lime and orange. On the basis of article 16 of plant protection developed by Iranian ministry of agriculture on 2004, citrus canker was considered a quarantine disease. In which the movement of infected plant parts are not allowed to be transferred out of following provinces, namely Hormozgan, Sistan and Baluchestan, Jiroft and Kahnooj in kerman, Ghir and Karzyn in Fars. Canker can be controled under conventional and new techniques. Chemical pesticides do have adverse effects on ecosystems, human health and livestock. New methods include bacteriocins, antibodies, bacteriophage and aptamer. Aptamers are oligonucleotides, consisting of DNA, single stranded RNA or peptide molecules. They can bind to a target molecule with high affinity and specificity. Citrus canker cause by Xanthomonas citri subsp. citri, which is divided into 5 groups. Among which type A and "A" ^"*" damage citrus in Iran. PthA is avrBs3/pthA family that has significant effect on the bacteria. Mutations in the effector molecules, affects pathogenicity. This study aimed to clone and express the aptamer YPASYMQ in tobacco plant to reduce the impact of pthA. The results showed the leaf tobacco cultivar Xanthi, Benthamiana and Citrus latifolia, Citrus sinensis and Citrus aurantifulia 3 days after expressing aptamer YPASYMQ was injected with pthA have significant difference compare with control (only protein pthA) in response HR and symptoms the canker. But there was no significant difference in Brassica napus. Aptamer could reduce pthA protein and Western blot test results, aptamer in 11 days after the exxpression is exist but its value is reduced.