Leaves of Juglans regia L. collected from two different locations [Adana (A) and Ankara (BA from Turkey were subjected to hydrodistillation in a Clevenger type apparatus to yield the essential oils (EOs). GC/MS and GC-FID analyses revealed that the A EO was rich in thymol (23.1%), while caryophyllene oxide (33.8%) was found as the main constituent of B EO. Both contained beta-eudesmol (1.4% - 9.5%), (E)-geranyl acetone (3.7% - 5.8%) and the eudesmane type constituent juglaterpene A (3.1% - 11.0%). Using a HP Innowax preparative capillary column connected to a preparative fraction collector, an unknown constituent, juglaterpene A (1, 11-hydroxy-2,4-cycloeudesmane), was isolated in a rapid one-step manner with > 94.0% purity. Structure determination was accomplished from 1D- and 2D-NMR spectroscopic data. Oil B demonstrated significant larvicidal activity against 1st instar Aedes aegypti L.