The research work was conducted to determine the seroepidemiology and pathology of mycoplasmosis and salmonellosis in chickens of some selected poultry farms situated at Chatkhil, Noakhali of Bangladesh. A total of 273 serum samples were collected and tested by serum plate agglutination test both for detection of Mycoplasma and Salmonella infections. For the pathological study 5 Mycoplasma seropositive and other 5 Salmonella seropositive live chickens were collected randomly from the farms and sacrificed for necropsy and pathology. Seroprevalence of Mycoplasma and Salmonella infections were 55.6 and 27.1%, respectively. Seasonal prevalence of mycoplasmosis in summer and winter were 51.9% and 59.4% and salmonellosis in summer and winter were 30.4% and 23.8%, respectively. In post mortem investigation the lesions in Mycoplasma positive birds included slight congestion, dark unifocal to multifocal hemorrhagic spot with slightly fibrinous exudate on the lung, flaccid heart, pale and enlarged liver and severely dark, swollen spleen and slight hemorrhagic spot in the ovary with stalk formation. In histopathology the results were found to be mild focal to diffuse interstitial pneumonia with pluritis and proliferation of pneumocytes-II, infiltration of lymphocytes and macrophages and severe congestion and hemorrhage in lungs. In liver very few to small-scattered necrotic foci infiltrated with different type of inflammatory cells were found. The Salmonella seropositive birds showed pale liver, slightly hemorrhagic darker ovary with stalk formation. Microscopically, very few scattered necrotic foci infiltrated with different types of inflammatory cells in liver and mild chronic enteritis was observed. However, further studies should be conducted for isolation and identification of different Mycoplasma and Salmonellae, determination of their immunogenic variation and establishment of vaccine with isolated Mycoplasma and Salmonellae.