Thirty pigeon were collected to study the most common lesions of respiratory system from 1/12/2010 to 1/3/2011, and performance the post mortem examination on these pigeons. The study demonstrate presence of respiratory clinical signs represent by sneezing, rales, respiratory distress, watery or mucoid nasal discharge and other clinical signs such as ruffled feather, loss of appetite, loss of ability of flying, watery or greenish diarrhea, restlessness, torticollis and mostly death. The most prominent gross pathological lesions were 43.3% of studied pigeons include congested pharynx, hemorrhage of larynx and congested of trachea. Petechial hemorrhage with congestion of bronchus and lung. 3.3% show tracheal and bronchus congestion, petechial hemorrhage on lung and opacity of air sacs with thickening. The prominent histopathological lesions observed about 26.7 % of lesions characterized by the presence of hemorrhage in mucosa of larynx, vaculler degeneration of epithelial cells of mucous gland in trachea and sloughing and desquamation of mucosa, hemorrhage in mucosa and congestion of blood vessels of trachea. In bronchus presence of congestion of blood vessels and hemorrhage inside the bronchi. In the lung hemorrhage in the interstitial tissue and emphysema, 3.3% of lesions observed hemorrhage and hyperplasia of epithelial cells of larynx. Vaculler degeneration of epithelial cells of mucous gland in trachea, hemorrhage and thrombosis in bronchi with inflammatory exudate. In lung sever hemorrhage in the interstitial tissue with thickness of alveolar wall, hemorrhagic air sacs and thickened. This study conclude presence of sever pathological lesions in the lower respiratory system of pigeons due to infection with different diseases either bacterial diseases such as air saculitis, infectious coryza, or viral diseases like infectious bronchitis, infectious laryngotracheitis, Newcastle disease, circoviral infection, or mycoplasmosis and chlamydiosis, and also may be non infectious causes like increase ammonia level.