Abstract: The present study investigated the inhibitory range of antifungal substances (AFS) produced by Coniothyrium minitans against different phytopathogenic fungi and its stability under heat, acidic or alkaline conditions, and ultraviolet (UV). The results showed that the AFS could greatly inhibit the mycelia growth of the 10 tested fungi, including Sclerotinia sclerotiorum, S. trifoliorum and S. minior, and was heat-stable. The AFS heated at 120℃ for 30 min could inhibit mycelia growth of S. sclerotiorum by 49.5%. pH could affect the activity of AFS against S. sclerotiorum. The highest activity of AFS was observed under pH 7. The AFS was generally stable under different pH values (pH 1 to 14), but was more stable under acidic conditions (pH 1 to 6), with the inhibition of mycelia growth ranging from 81.1% to 76.4%. The stability of AFS could be affected by UV-irradiation when it was spread on leaves of oilseed rape. Based on these results, the AFS was concluded as stable substances, and considered to be of potential for control of rapeseed stem rot caused by S. sclerotiorum.