Citrus production is estimated about 4 million tons in Iran and its decay is about 28-31 percent. So, huge amounts of precious citrus product are decayed every year. Black rot is one of citrus post harvest diseases which starts from orchard and can cause huge damages in storage. As the weather condition is not suitable in Kerman province, the disease damages is not considerable. But rain falls and cool weather in winter 2016 caused remarkable damages especially on orange and tangerine fruits. To study causal agent of the disease, samples were collected from contaminated fruits. Samples were placed in Petri dishes containing potato dextrose agar (PDA) medium. Petri dishes were incubated at 25 °C in the dark for one week and the fungus purified using the single-spore method. Pathogenicity tests were performed based on Koch’s postulates on healthy fruits. Molecular investigation using OPA10-2 primer showed that causal agent of the disease is Alternaria alternata. Streptomycetes have characteristics that make them suitable for biocontrol ofplant diseases. They are capable ofproduction of secondary metabolites such as enzymes, antibiotics and active biological products which have commercial value. Many isolates of Actinomycetes isolated from Kermansoilsby using a selective medium, casein glycerol agar (CGA).Two isolates of Streptomycetes (isolates17 and 53)having inhibitory characteristic against the pathogen could suppress Alternaria alternataboth in dual cultures on PDA plates and on healthy tangerine frui5ts.Fruit tests arranged 3 times in 6 treat ments and one treat ment with no incubation was kept as witness. This study is the first report of Alternaria alternata as causal agent of citrus black rot in Kerman province.