Rice is an important food crop in the world. Bacterial leaf blight, caused by Xanthomonas oryzae pv. oryzae, is one of the important diseases of rice that is prevalent in different cultivars in the world. Identifying and planting resistant or semi-resistant cultivars is the most effective method of disease management. This study aimed to investigate the reaction of four Iranian rice cultivars; Shiroodi, Setayesh, Fajr, and Hashemi, to the disease under field conditions. Rice plants with the disease symptoms were sampled from different regions of Kohgiluyeh and Boyer-Ahmad province in southwestern Iran, during 2012-2013. The pathogen was isolated from infected leaves after their surface disinfection, on Yeast extract-dextrose-CaCO3(YDC) medium. The isolated bacterium was rod-shaped, gram-negative, obligate aerobic, oxidase negative, catalase positive, levan and lecithinase positive. It induced a hypersensitivity reaction in tobacco leaves and could not hydrolyze starch, but it hydrolyzed gelatin, ascoline, and Tween 80. Based on a comprehensive analysis of morphological, biochemical, pathogenicity, and genotypic traits, the pathogen was identified as X. oryzae pv. oryzae. The reaction of these four Iranian rice cultivars to the disease was evaluated by inoculating them with the pathogen, monitoring the progression of disease symptoms, and measuring the growth of the bacterial population in each cultivar. There was a significant difference among the cultivars in terms of the length of leaf necrosis and the bacterial population within the tissue, with the Hashemi cultivar exhibiting the highest sensitivity and the Shiroodi cultivar showing the lowest sensitivity to the disease. The occurrence of bacterial leaf blight disease in Kohgiluyeh and Boyer-Ahmad province, as well as the reaction of these cultivars to the disease, are being reported for the first time.