Abstract: The mechanism of camptothecin (CPT) against Botrytis cinerea was studied by conductivity method, UV spectrophotometry and electron microscopy in this paper. The results showed that the membrane permeability of B. cinerea increased 30.7%, extracellular protein concentration increased 13.5% after 200 mg/L CPT solution treatment. The sugar and soluble protein content of B. cinerea increased firstly, especially in 0-1 h and then decreased with the growth of the processing time, and finally tended to flatten after CPT solution treatment. The hyphae malformed with swollen or constriction and the growth point of mycelial constricted after CPT treatment. At the same time, the cell cavities and mitochondrias increased, the vague cristae mitochondriale and the degradation of nucleus appeared.