Mycoplasmosis causes important economical losses in poultry industry. So far, 23 mycoplasma serotypes have been isolated from avian species, and Mycoplasma gallisepticum(MG), Mycoplasma synoviae(MS), Mycoplasma meleagridis(MM) and Mycoplasma iowae(MI) are known as the most pathogenic strains. Mycoplasmas generally cause disease in respiratory systems of poultry. This review summarizes the knowledge on the diagnosis and epidemiology of avian mycoplasmosis.