Abstract: Ornithobacterium rhinotracheale (ORT) infections cause major losses to the poultry industry. In search for factors implicated in the pathogenesis of ORT infections, the role of outer membrane proteins (OMPs) in the interaction of ORT with chicken tracheal epithelium was investigated. For this purpose, immune sera were prepared against total extracted OMPs, whole cell bacteria and three major OMPs of 45, 53 and 70 kDa and used in bacterial adherence inhibition assay. The results showed antibodies against a 53 kDa OMP significantly (p<=0.05) inhibited the bacterial adherence to chicken tracheal epithelium up to 78%.