Abstract: The aims of the present study were to isolate and serotype, determine the Seroprevalence, Drug susceptibility and diagnosis of infection by Polymerase Chain Reaction (PCR). In this study 460 serum samples and 220 tracheal swabs, 90 ovaries and oviduct swabs, 90 misshapen egg shells swabs were collected from 22 broiler breeder flocks of 5 companies. Serological results showed that all of the 22 flocks (100%) were positive for ORT infection. Ornithobacterium rhinotracheale (ORT) antibodies were detected in 289 (62/83%) out of the 460 serum samples. ORT was detected from tracheal swabs of seven flocks (31/81% or 3/18% out of 220 tracheal swabs). There was significant correlation between flock different ages and ORT titers (p<0.05), but correlation of flock ages and ORT isolates was not significantly different (p>0.05). Seven flocks infected with ORT were detected positive in PCR but bacteria were Isolated from only five culture. No ovaries and oviducts, misshapen egg shell swabs yielded ORT. A 784 bp fragment of the 16S rRNA gene was amplified using ORT specific primers in the PCR. All the isolates were identified as serotype A by Rapid Agglutination Test. Drug sensitivity test using standard disk diffusion technique was performed with 27 antibiotics. Antibiotic susceptibility for Quinolons family was seen more than the others and Cephalosporins family except to Cephalexin. The isolates were 80-100% susceptible to Tetracycline family and the most antibiotic resistant were seen for Aminopenicillins, Polypeptides, Sulfanamides and 80-100% resistant to Aminoglycoside family. Eighty percent of the isolates were resistant to Licomycin and 60% were moderate sensitive to Lincomycin. This study is the first report of prevalence of ORT, bacterial isolation, biochemical characteristics, serotyping and molecular method (PCR) in broiler breeder flocks in Guilan province of Iran.