Postharvest diseases reduce postharvest quality and limit storage period of fruit. One of the alternative methods against the postharvest diseases is to use gamma irradiation. In this study, ten P. expansum isolates were collected from „Golden Delicius‟ apples in cold storages of Kayseri. According to pathogenicity test, O2 isolate of P. expansum was found as the most virulent isolate and used in the experiment. In vitro, cultures were irradiated with 60Co gamma sources (with dose rate of 0.668 kGy h-1and specific radioactivity of 1026.2 Curie), incubated at 34ºC and 23±1ºC. At 27th day while mean the colony diameter of untreated cultures was 25.87 mm, the cultures treated with 3.0 kGy had a diameter of 9.12 mm in 3-4ºC. Similarly, at 9th days 3.0 kGy treated cultures and untreated cultures had a mean colony diameter of 37.50 mm and 54.87 mm, respectively, at 23±1ºC. The optimum dose was 3.0 kGy for both incubation temperatures. Differences between doses were also significant at p< 0.05 level. The area under the disease progress curve (AUDPC) was calculated for each individual treatment and observation day in vitro. Confirming statistical analysis, the lowest AUDPC value was found at 3.0 kGy treatment