Rice (Oryzae sativa L.) is the second human food source after wheat, cultivated in more than 60 countries around 150 million hectares. This important and strategic product has been infected with many pathogens that reduce the quantity and quality of the product. One of the most important diseases of rice that has been observed in our country in recent years is the bacterial blight of rice caused by Xanthomonas oryzae pv. oryzae. In the present study resistance of Lenjan, Hashemi, Firouzan and Gilane cultivars to the bacterial blight disease was evaluated. Bacterial suspensions were prepared from 107 cells/ml of fresh bacterial culture and After 30 days of germination of seeds, rice leaves were sprayed with suspension of bacteria. To determine the bacterial population, half a gram of leaf tissue of the tested plants was weighed separately and completely crushed in a mortar. Then, the extract was obtained from dilution series and made from appropriate culture dilutions. The sampling from different leaves of rice varieties was carried out at four, eight, twelve, fourteen and sixteen days after inoculation The results of bacterial population dynamics and pathogenicity showed that population log was different in various cultivars and pathogenicity in each cultivar. Based on the combination and comparison of the overall results of the two tests, Hashemi had the highest population and severity of disease and was considered as the most sensitive cultivar, and Lenjan cultivar with the lowest disease severity and bacterial population as a highly resistant cultivar. In Gilaneh and Firouzan cultivars, no significant difference was observed, and in terms of disease severity, Firouzan resistant and Gilaneh were introduced as relatively resistant.