The essential oil obtained by steam distillation of the herbs of Jeju Agastache rugosa has shown significant DPPH radical scavenging activity. For the elucidation of its volatile components, the essential oil was analyzed by GC-MS. Each component was identified by GC or mass spectral analysis. The compounds identified were as follows: pulegone, L-menthone, DL-limonene, isopulegone, beta-caryophyllene, beta-myrcene, and estragole. Several abundant components with phenylpropanoid-type structures may have contributed to the activity. The results suggest that the essential oil may be suitable for development as a food preservative and alternative antioxidant.