Xanthomonas translucens causal agent of Bacterial leaf streak (BLS) is prevalent and important pathogens of family Poacea in Iran. X. translucens pathovars including secalis, cerealis, hordei, translucens and undulosa are separated by domain hosting on members this family. Pathovars hordei and cerealis have been reported from different regions of Iran. Symptoms on leaf were light brown water water-soaked lesion, with a few centimeters long that were becoming longer gradually. Primary symptoms were translucent stripes that were observable under incident light. Bacterial leaf streak on barley (Hordeum vulgare) observed in fields of Kerman province in April 2017. In order to isolate and identify the causative agents of pathovars in Kerman province, Sampling was performed on wide and complete scale from infected fields. Bacterial isolates obtained on sucrose nutrient agar (NAS) from leaf streak and water-soaked symptoms. The isolates were yellow on YDC agar, gram negative, Catalase positive, negative oxidase, strictly aerobic and show positive High-sensitivity reaction on tobacco. They did not have the ability to grow at 37 ° C .All isolates used from D- fructose, D-glucose, D- xylose, L- arabinose, sucrose, trehalose, , mellibus, mannitol, palatinose and lactose as carbon sources for growth. None of the isolate could utilize inositol, ribos, rhamnose, Sorbus, sorbitol, tartaric acid, glycolic acid and Galactonic acid. Pathogenicity tests performed on greenhouse. Bacterial suspensions in MgCL2 10 mM solution with Density (1 × 106 CFU/ml) inoculated into barley leaves. After ten to fourteen days, symptoms disease were created including state of water water-soaked and necrosis on the leaves. No symptoms were observed in leaves inoculated with MgCL2 10 mM solution considered as control. For detection isolates as X. translucens group, DNA was extracted by the phenol chloroform method with a little change and used in PCR with T1 and T2 primer. The PCR result was reproduce an expected DNA fragment of 139 bp among the isolates. Regions of rpoD and gyrB housekeeping genes, amplified whit XrpoD1F / XrpoD1R and XgyrB1F/ XgyrB1R primers and two pieces of 875 and 865 base pairs were reproduced among the isolates, respectively. The replicated parts were sequenced by Macrogen company (South Korea), then their sequence deposited in GenBank database. Sequence compression indicated that the isolates have the highest identity (99%) with X. translucens pv. undulosa. This is First Report of X. translucens pv. undulosa , Bacterial Leaf Streak agent on barley in Iran