Plants can defend themselves against fungal infection by natural means induced by biotic and abiotic elicitors. Osthol is a natural compound extracted from dried fruits of Cnidii Monnieri Fructus. In this study, it has been shown to not only be a fungicide with acceptable curative properties ( control efficacy of 68.72), but it also showed a significant prophylactic effect ( with control efficacy of 77.36) against pumpkin powdery mildew at a concentration of 100 mu g center dot mL(-1). In pumpkin leaves with/ or without inoculation of Sphaerotheca fuliginea, osthol treatment induced the accumulation of chitinase and peroxidase and enhanced the transcription of chitinase gene in non- inoculated leaves. The potentiation of phenylalanine amonia- lyase activity in leaves by osthol application and following inoculation was absent in that with inoculation or osthol treatment, indicating that induced PAL in osthol- pretreated plants was inoculation- mediated. In conclusion, this natural compound could induce resistance response in the plant against powdery mildew.