In April of 2003 to 2004, the gray mold disease caused by Botrytis cinerea on Hypericum ascyron was occurred in the exhibition field of Gyeongsangnam-do Agricultural Research and Extension Services, at Hamyang-gun in Korea. The disease symptoms were started with water-soaking lesions in stem and the infected plants became withered, discolored and died. The conidia and mycelia of the pathogen appeared on stems of infected plants. The conidia were 1-celled and mostly ellipsoid or ovoid in shape and their color was light gray. The size of conidia was 4~16 × 3~8 µm and that of conidiophores was 12~26 µm, respectively. The pathogen formed sclerotia abundantly on potato-dextrose agar. The optimum temperature for sclerotial formation was 20 oC. Pathogenicity of the causal organism was proved according to Koch’s postulate. The causal organism was identified as Botrytis cinerea based on mycological characteristics. This is the first report on gray mold of H. ascyron caused by B. cinerea in Korea.