The insecticidal activity of materials derived from the rhizome of turmeric, Curcuma longa, against four agricultural and four stored-product insects was examined using direct contact application method. The biologically active constituent of the Curcuma rhizome was characterized as the sesquiterpene ketone ar-turmerone by spectroscopic analysis. Potencies varied according to insect species and dose. In a test with Nilaparvata lugens female adults, ar-turmerone caused 100 and 64% mortality at 1,000 and 500 ppm, respectively. Against Plutella xylostella larvae, the compound gave 100 and 82% mortality at 1,000 and 500 ppm, respectively. Against Myzus persicae female adults and Spodoptera larvae, ar-turjmerone at 2,000 ppm was effective but weak insecticida activity was observed at 1,000 ppm. At a dose of $2.1 extrm{mg}/ extrm{cm}^2$, ar-turmerone was almost ineffective (<10% mortality) against adults of Sitophilus oryzae, Callosobruchus chinensis and Lasioderma serricorne as well as larvae of Plodia interpunctella. the naturally occurring Curcuma rhizome-derived ar-turmerone merits further study as potential insect-control agents of as lead compounds.