Анотация: The aim of this study was to determine the prevalence of seropositive broiler flocks against Ornithobacterium rhinotracheale (ORT) and biochemical identification of this bacterium in Mazandaran province, north of Iran. Tracheal and serum samples were collected from 45 broiler flocks at farms and slaughter houses. From 450 tracheal samples, 12 (2.6 percentage) ORT isolates were identified using biochemical tests. Of the 450 serum samples, 320 (71.1 percentage) samples were positive for antibodies to ORT by ELISA. Results of this study indicated the presence of ORT and high prevalence of antibodies against ORT infection in north of Iran