Abstract:By means of rotatory belt fractional distillation, LC, HPLC, PGC and derivative methods, 27 compounds were separated from the essential oil which isolated from Zanthoxylum avicennae (Lam.) DC. by stream distillation. Twenty two of them were identified by the methods of IR, GC/IR,, 1H-NMR,18C-NMR, GC/MS/DS and the preparation of derivatives. Among them, 4-methyl-6-acetoxyhexanal was first found in nature. Fifteen compounds have been tested their antimildew activities. Citral, l-octanol, 4-methyl-6-acetoxyhexanal and linalool showed strong activities. The relationships between the structure of compounds of essential oil and their respective antimildew activities are also dealt with in this paper.