Abstract: In this study, twenty isolates were randomly chosen from the population of Sclerotinia sclerotiorum（S. sclerotiorum）（n=10） and Sclerotinia minor（S. minor）（n=10）. They were collected from the same sunflower field in Inner Mongolia region and compared for the difference in biological characteristics and pathogenicity. Our data indicated that after incubation on PDA at 23 ℃ for 3 days, the average diameters of S. sclerotiorum and S. minor colonies were 8.3 cm and 5.3 cm, respectively. The average yield of oxalic acid（OA） and polygalactourase（PG） activity of S. sclerotiorum isolates were 27.67 μg/mg mycelia and26.87 U/mg mycelia, respectively; for S. minor, those were 18.91 μg/mg mycelia and 21.58 U/mg mycelia, respectively. The sclerotial initiation and number of sclerotial of S. minor were much earlier and higher than that of S. sclerotiorum. The pathogenicity was also compared by using detached leaf assay. Our results indicated that the average lesion size at 2 days post inoculation of S. sclerotiorum was 3.11 cm which was significantly larger than that of S. minor（1.71 cm） at 0.05 significance level. In conclusion, except for the sclerotial formation, the S. sclerotiorum isolates showed higher growth speed,PG enzymes activity and pathogenicity compared with S. minor collected from the same sunflower field.