The essential oils hydrodistilled from roots and rhizomes of Curcuma alismatifolia Gagnap. from Thailand were analyzed by GC-MS technique. (-)-Xanthorrhizol (52.37%) and gif.latex?\beta-curcumene (42.00%) were found to be the major components in the root and rhizome essential oils, respectively. Antioxidant activities of both essential oils were evaluated using five different methods including DPPH radical scavenging assay, hydroxyl radical scavenging assay, hydrogen peroxide scavenging assay, ferrous ion chelating assay and ferric reducing power assay. Lascorbic acid and EDTA were used as a positive control. The DPPH radical scavenging activity and ferric reducing power of the root and rhizome essential oils were insignificantly different as compared with L-ascorbic acid while the hydroxyl radical scavenging activity of the rhizome essential oil was significantly higher than those for the root essential oil and L-ascorbic acid. The root and rhizome essential oils exhibited weaker activities for scavenging hydrogen peroxide molecules and chelating ferrous ions, as compared with L -ascorbic acid and EDTA, respectively.