Survey on developmental stages of Myxobolus karuni and M. persicus in the gills of Barboid fishes from Mezopotamian part of Iran was done. A total 296 fish specimences were examined. Random sampling was carried out during 2002- 2004 from Karoun, Karkheh Rivers and Shadgan Lagoon. The fishes transported alive to the laboratory, their gills were fixed and stained. Myxobolus karuni developed histozoic, the plasmodia were found inside the blood vessel, it developed in the epithelial cells of primery filaments, the spores are large and ellipsoidal in shape. M.persicus starts and finished the plasmodia in epithelial and endothelial of the secondary filaments, the spores are oval in shape. Up to now, the location of infection of few species of gills Myxobolus Spp. are known. According the results of this study Barbus pectoralis, B. barbulus and B. esocinus are new hosts for Myxobolus karuni and M persicus.