Efforts were directed to study 720 diseased chickens (broilers and broiler breeders) taken from 40 flocks with variable clinical signs including mild to severe respiratory manifestations either alone or associated with growth retardation, arthritis, nervous signs and lamenees preceded by increase of mortalities. The mortality rates varied between 0.2% and 16.8%. Ornithobacterium rhinotracheale (ORT) was isolated from 23 out of the 40 flocks (57.5%) and were recovered from various organs including lungs, trachea, air sacs, joints, sinuses, brains and yolk sacs of recently dead and diseased birds, while no strains could be isolated from heart blood, pericardium, liver and eyes. It could be isolated also from hatcheries that suffered from lower hatchability, increased late embryonic death and dead in shell chicks. The serotyping of the isolates by AGPT revealed that, they all belonged to serovar A. the sensitivity test against antibiotics of the 23 isolates of ORT revealed that 100% of the isolates were sensitive to ampicillin, amoxicilline oxytetracycline,ciprofluxacine and chloramphenicol, while all of them were resistant to gentamycin, streptomycin, colistine and sulphamenthoxazale-trimethoprim. Inoculation of S.P.F embroynated chicken eggs by ORT isolated strains revealed that there were no characteristic lesions in embryos except some congestion in the head and neck of the embryos. Also they could be isolated from the yolk sac of newly hatched chicks.