Bacterium Xanthomonas arboricola pv. pruni (Xap) is one of the most important bacteria causing leaf spot on stone fruit trees. This bacterium is considered as a quarantine bacterium. It was first reported in 2004 from the stone fruit trees of the Giulan province and in 2015 from Razavi Khorasan province following frequent rainfalls. The present study was conducted to evaluate some of the pathogenicity factors of 20 Xap strains have been obtained in 2015 and to determine their possible relationships with the virulence of the bacterium. The pXap41 carries genes that effect on pathogenicity and virulence of Xap strains. The XopE3 effector is unique to the pruni pathovar, and XopA effector is shared among the economic pathovars of arboricola species such as mentioned one. The formation of bacterial aggregations (biofilm) is also involved in the expression of pathogenicity-related factors and caused bacterium maintenance under unfavorable conditions. The presence of surfactant and xanthan may be affected the bacterial spread and growth in hard conditions, respectively. The production of cell wall degrading enzymes can also play a role in bacterial penetration into the tissue and can be considered as a pathogenicity factor. In the current study, the pathogenicity of the strains was investigated in laboratory and greenhouse conditions and compared on sensitive prunus leaves of Santa Rosa. The presence of a specific plasmid, pXap41, the existence of XopE3 and XopA effector genes, type of motility including swarming, swimming and twitching, surfactant production, biofilm and xanthan formation, as well as the production of pectate lyase, polygalactoronase, cellulase and protease enzymes was also evaluated. In all tests, reference strain, ICMP7485 was used as positive controls. During the molecular experiments, it was found that all strains have XopE3 and XopA genes, and pXap41. In the case of motility in bacteria, virulent strains exhibited the dendric growth. The highest levels of surfactant were recorded 5 cm halo in oil spread method. The amount of biofilm formation was variable among strains. The highest biofilm formation was measured 0.29 at the wavelength of 570 nm. It seems there is relationship among bacterial virulence, biofilm formation and surfactant production. The presence of xanthan was also proven in all studied strains. The more virulent strains were secreted more cell wall degrading enzymes. The existence of specific and efficient pathogenicity factors in Xap strains, may be influenced bacterial penetration, pathogenicity and virulence on the stone fruits