Eighty samples were collected from freshly dead hatched chicks, also one hundred and forty freshly dead layers 8-12 month old age were collected (35 samples from joint, 35 from oviduct, 35 from brain and 35 from lung, trachea and air sac) from different farms in Assiut Governorate. Ornithobacteriun rhinaotracheale organism was isolated at a rate of 40% from newly hatched chicks and at a rate of 17%, 22.8%, 8.5% and 34% from joint, oviduct, brain and lung, trachea and airsac respectively. Experimental infection of 30 days old chicks by isolated organism through intravenous and intraairsac inoculation was done. Intravenous inoculation leads to depression, ruffling feather of the infected birds and decreased body weight, eye affection, difficult in breathing, nasal secreation and some birds showed nervous signs before death which reached to 30% in the 3 and 4th day after infection but in the 2nd week postinfection some birds revealed arthritis and could not stand. Postmortem examination revealed airsacculitis, perihepatitis, pericarditis, pneumonia and oedema of the lung. Some birds showed caseous, yellow material on the abdominal airsacs, and others revealed congestion in the brain. Birds which inoculated intra airsac showed also the same previous signs and lesions but it appeared at longer time. Reisolation of the organism from experimentally infected birds was succeeded. Sensitivity test revealed that amoxycillin, tetracycline and enrofloxacin were the most effective drugs. The aim of this work is designed to cover the following points: - Isolation and identification of the Ornithobacterium rhinotracheale organism and its incidence in the newly hatched chicks and layers. - Experimental infection of the isolated organism to 30 days-old chicks. - In vitro sensitivity test of the isolated organism to some antimicrobial drugs.