The present study was carried out to investigate the pathology of avian aspergillosis in commercial broiler chickens at Chittagong district. A total of 912 sick and dead chickens were collected from 20 commercial broiler farms and diagnosed for avian aspergillosis on the basis of clinical signs, symptoms and postmortem findings. The suspected birds were collected for necropsy examination and mycological culture. Gross lesions of multiple hard creamy to yellow colored, circumscribe plaques throughout the lungs surface and consolidated lung with necrotic areas were observed. Microscopically, the typical nodules consisted of caseous necrotic center were present. Identified the Aspergillus spp according to their color of colony growth on Potato Dextrose Agar media. The overall incidence of avian aspergillosis was found 6.14%. Among five Upazilla, significantly (p<0.007) higher and lower incidence was found in Patenga and Sitakunda that were 9.25% and 3.43% respectively. It was observed that highest incidence (8.22%) in rainy and lowest (3.16%) in winter but moderate (5.16%) in summer season. The disease was significantly (p<0.050) higher (8.27%) in age between 6-10 days and lower (4.11%) in age between 0-5 days. It was also found that incidence of avian aspergillosis was significantly (p<0.042) higher in flocks reared on sawdust litter (7.69%) as compared to rice husk litter (3. 46%).