Abstract: Effect of 5-(4-chlorophenyl)-2,3-dimethyl-3-(pyridine-3)-oxazoline (SYP-Z048) on different developmental stages of Botrytis cinerea was investigated by bioassay. The results showed that SYP-Z408 had significant inhibitory activity on colony growth, germ tube elongation, conidial and sclerotial production of B. cinerea.The EC50 value of SYP-Z048 against colony growth and germ tube elongation of strain P-9 was 0.193 and 0.059 μ g/mL, respectively. SYP-Z048 can inhibit colony growth and germtube elongation of B. cinerea by more than 77% at the concentration of 0.5 μ g/mL. However, it can only inhibit conidial and sclerotial germination by less than 10% and 40% at the same concentration, respectively. This result suggested that SYP-Z048 had little effect on conidial germination. The analysis of ultraviolet absorption revealed that SYP-Z048 could disrupt the cellular membrane structure, and caused the leakage of intracellular nucleic acid and protein from B. cinerea. The lesion extension of B. cinerea on tomato leaves could be inhibited effectively by 120 μ g/mL of SYP-Z048, and the inhibitory rate was 83.74%.