At this study, it was aimed to determine the effect of Trichoderma isolates that was isolated from the soil samples taken from the different regions on black scurf and stem canker disease caused by Rhizoctonia solani Kuhn that has been one of the biggest problems of the potato cultivation. At the end of the soil isolations, totally 81 Trichoderma isolates were obtained and their species were identified. Of these isolates, T. harzianum (42%), T. virens (31%), T. asperellum (15%) and T. viride (12%). All of the isolates were tested in vitro for their antagonistic activity against the R. solani isolate. The isolates that show high inhibition rate was selected and tested against R. solani in vitro. Potato plants were grown in a greenhouse for about 10 weeks. Then the plants were evaluated according to the scale, plant height, shoot fresh and dry weights, root fresh and dry weights were noted. The experiment was conducted two times in three replications. At the in vitro tests, generally, it was determined that Trichoderma isolates have inhibited to R. solani and in vivo, they were reduced the effects of the disease and they were raised the development of the plant. In particular, it was determined that some isolates of the T. harzianum and T. virens have reduced the severity of the disease. It was determined that both in vitro and in vivo isolates have shown different efficiency against R. solani.