The present study was conducted to describe the gross and microscopic lesions in lungs due to chronic respiratory disease of chickens in Ayodhya district of Eastern Uttar Pradesh with special reference to immunohistochemical diagnosis. The naturally dead birds from 10 different private farms in Ayodhya district of Eastern Uttar Pradesh were collected for 6 months (October, 2018 to March, 2019). After post-mortem examination, the grossly suspected lungs were kept for further histopathological and immunohistochemical study. Macroscopic lesions in lungs showed yellowish to creamy thick coverings. On removal of superficial coverings, lungs revealed dark red colour appearance and showed congestion and haemorrhages. Microscopically, lung showed oedema in the lumen, congestion of capillaries and lymphocytic infiltration in the interstitial tissue. MG antigen was evident as brown colored staining of parabronchiolar epithelial cells, primary bronchiolar epithelial cells besides inflammatory cells in immunohistochemical studies.