Currently, the poultry industry has an important position in producing protein products. On the other hand, it is necessary to identify diseases specific to a region that lead to poultry loss in that region. We aimed to assess the serology of broiler flocks with high mortality rates in southern Iran during 2014-2015. After the referral of 40 insured poultry owners experiencing high mortality rates, serum samples were obtained in two stages with 2-week intervals. 3200 serum samples were collected from broiler farms in southern Iran during a 2-year period and transferred gradually to the laboratory. Influenza, bronchitis, and Newcastle viruses were the most important causes of infection and the mean amount of mortalities was 25%. Also, influenza was the most important factor leading to mortality in the region. On the other hand, the low virulence influenza strain and the bronchitis virus were accompanied by secondary infection and mycoplasma. In southern Iran, the organisms causing the highest rate of infection were the influenza and bronchitis viruses.