Abstarct: Aerobic mextabolisms, including photosynthesis and respiration, used to be considered as the sole sources of reactive oxygen species (ROS) generation.It is known for quite some time that plants actively produce these molecules, which may control many different physiological processes such as abiotic and biotic stress response, and systemic signaling. Common bacterial blight of bean caused by Xanthomonas axonopodis pv. phaseoli (Xap); is a sever and devastating disease in both temperate and tropical production zones. It causes yield losses by about 40%. Cellular responses of bean to Xap baxsed on transcxript analysis of enzymes involved in both ROS production and scavenging were analyzed. Inoculated leaves with Xap were used to study the transcxript changes of the genes via RT-PCR. NADPH Oxidase and APX inclined significantly at 12 h post inoculation (hpi) followed by a sharp increase at 24 hpi. SOD and MDHAR was continuously rocketed. In contrast, CAT exxpression showed an enhancement at 12 hpi and a decrease at later stage .