One hundred and ninty-six Sclerotinia sclerotiorumstrains from Changde and Yiyang of Hunan province were isolated and purified. Virulence of these strains was measured by inoculating detached leaves. The results showed pathogenicity differentiation of these S. sclerotiorum strains from the two areas was apparent. Using CF cellulose, dsRNA extraction were conducted on 19 hypovirulent strains, dsRNA screening showed that dsRNA were extracted from 3 strains (CY019, CY080 and YY077). CY019 has an abnormal phenotype with sparse hyphae and low production of sclerotia. A dsRNA-free strain CY019VF was obtained from CY019 using hypha tip isolation and showed the restored pathogenicity by in vivo inoculation in rape stem. These results indicate the attenuated virulence of strain CY019 could relate to its dsRNA.