The volatile oil extracted from Syinga Juliana C.K.Schneid.by microwave pretreated and simultaneous distillation and extraction method was determined by the GC-MS.Phenol,2-methoxy-3-[propenyl](relative contents 62.21%),Phenol,2-methoxy-4-[2-propenyl]-,acetate(relative contents 17.7%) and Bicycleundec-4-ene,4,11,11-trimethyl-8-methylene-(relative contents 15.29%) were their chief components.The volatile oil showed significant anti-microbial activity to 6 bacteria and 4 fungi with the minimum inhibitory concentration(MIC) to Staphylococcus aureu(6.25 mL/L),Aspergillus niger(6.25 mL/L),Penicillum Citrinum Thom(6.25 mL/L),Proteus vulgaris(12.50 mL/L),Bacillus cereus(12.50 mL/L),Escherichia coli(12.50 mL/L),Salmonella(12.50 mL/L),Aspergillus flavus(12.50 mL/L),Saccharomyces cerevisiae(12.50 mL/L)Bacillus subtilis(25.00 mL/L) respectively.