Bronchopneumonia is one of the most important ovine diseases in Iran. This disease can be due to bacteria, viruses and parasites. In the ruminants pulmonary worms are the most prevalent cause of this disease. This study was conducted to diagnose the infestation rate of pulmonary worms in small ruminants of East-Azarbaijan. One thousand fecal samples were collected from sheep of different regions of Tabriz (during one year 250 samples per season) and tested for the first stage of respiratory nematodes larvae by bearmann apparatus. Furthermore, 400 lungs of slaughtered sheep were inspected and adult worms were isolated in the laboratory and recognized by diagnostic keys. Results showed that 56.9% of the fecal samples were infested. Infestation rate of sheep to Dictyocaulus filarial, Protostrongylus rufescens, Muelerius capillaries and Cystocaulus ocreatus were 28.9 %, 12.7%, 29% and 29.4%, respectively. Significant difference was observed in the rate of infestation according to seasons by ANOVA (p<0.05). In autumn, infestation rate was higher than the other seasons. Significant difference was observed in infestation level of approximate 2 years old sheep (p<0.05). Infestation rate of male sheep was higher than the female ones.Isolated worms from the 400 lungs which were inspected, were Dictyocaulus fillaria (34%), Protostrongylus rufescens (11%) and Cystocaulus ocreatus (32%). Muelerius capillaris was not observed. Infestation rate to lung worms in autumn was higher than the other seasons. It is suggested to prevent from and treatment of sheep according to high rate of infestation to lung worms in this area.