Abstract: The antifungal activity of cycloalkyl sulfonylureas N-(2,4,5-trichlorophenyl)-2-oxocyclohexylsulfonamide (compound 108 for short) against Botrytis cinerea was investigated in vitro. The results showed that compound 108 could inhibit different stages of B. cinerea including hyphal growth, spore production and germination, with EC50 values of 6.90, 4.70 and 4.11 μg/mL, respectively. The sclerotic production and pathogenicity of B. cinerea could also be inhibited by compound 108, and the hyphal could not produce sclerotia under 20 μg/mL of the compound. The pathogenicity of B. cinerea mycelia treated by compound 108 at 40 μg/mL was significantly lower than that of the control. Morphological and ultrastructural studies showed that compound 108 could cause hyphae collapse, deforming, and cell wall shrinkage, thickening and layering of B. cinerea.