Abstract: In this study, the biocontrol efficiency of isolated Bjerkandera adusta M-1 strain (BaM1) against Sclerotinia sclerotiorum was evaluated and the conditions required to optimize culture of BaM1 were determined. This work provides new technical data for the biological control to Sclerotinia stem rot. The inhibitory effects of BaM1 against S. sclerotiorum were evaluated by a dual culture assay and by a liquid culture experiment. In addition, the antagonistic and the mycoparasitic properties of antagonistic BaM1 against S. sclerotiorum were observed by optical microscope and scanning electron microscope (SEM). The thermal stability of fermentation broth of BaM1 was investigated under different temperature regimes. Subsequently, the liquid culture conditions were optimized according to the single factor test and response surface methodology (RSM). Based on that, the biocontrol efficiency of BaM1 against S. sclerotiorum in plants was investigated in a greenhouse pot experiment. It was found that the inhibition of S. sclerotiorum by BaM1 in the dual culture assay was as high as 67.9%, greater than the inhibition rates achieved by carbendazim treatment (22.7%) and thiophanate methyl treatment (31.4%). The inhibition rate of the BaM1 fermentation broth was up to 51.8% in the liquid culture experiment, which was also higher than in the two chemical treatments. BaM1 had an obvious antagonistic effect on S. sclerotiorum and the mycelia of both organisms changed when growing together. Hyphae of BaM1 pierced and penetrated the mycelium of S. sclerotiorum, resulting in swelling of S. sclerotiorum hyphae, deformation and even fracture, when viewed under the scanning electron microscope, thus showing a strong mycoparasitism. Furthermore, the inhibition rate of BaM1 fermentation broth remained above 35% after heated 30 min in the water bath at 80 ℃, which illustrated the thermal stability of BaM1 fermentation broth. The identified optimal liquid culture conditions were C/N of 7.5, pH of 4.7, culture volume 33% of bottle capacity, a culture time of 22 d, a rotation speed of 180 r·min^-1, and a culture temperature of 32 ℃. Under these conditions an inhibition rate of 80.9% was achieved for BaM1 fermentation broth. Moreover, the biocontrol efficiency of BaM1 against S. sclerotiorum reached 71.4% in the greenhouse experiment, compared to 53.2% with carbendazim treatment. In conclusion, as a biocontrol fungus, BaM1 had strong antagonistic efficacy against S. sclerotiorum, and the inhibition rate of the fermentation broth was enhanced when culture conditions were optimized. The biocontrol efficacy in a greenhouse experiment indicated good prospects for field use of BaM1 against S. sclerotiorum.