Field investigation in a chestnut plantation at Nagykanizsa county confirmed the presence of chestnut blight disease. Samples obtained from the infected trees exhibiting symptoms of chestnut blight were subjected to laboratory investigation. A total of 17 C. parasitica strains were isolated and a total of 3 vc type were identified after vegetative compatibility tests. The isolates were also tested using EU testers, and it was determined that NF4 (and its subgroup) belongs to EU3, NF6V (and its subgroup) belongs to EU12, and NF7 (and its subgroup) belongs to EU20 vc type. Apple virulence assay was conducted to observe the induction of cankers and oxalate production to identify the pathogenicity of the virulent and hypovirulent strains. It was expected that the hypovirulent and the converted strains would not induce prevalent necrosis on the artificial wound because of the lack of oxalic production. The virulent strains produced prominent necrosis on the fruit. The results of the virulence test confirmed that hypovirulence was indeed present indicated by the inability of the hypovirulent and converted to induce necrosis on the fruits. Finally, dsRNA was isolated by molecular analysis of the mycelium of the hypovirulent strains confirming the presence of the hypovirus responsible for hypovirulence in chestnut blight fungus Cryphonectria parasitica.