The essential oils from the leaves of Juglans regia, collected from Kathmandu, Nepal, and Juglans nigra from Huntsville, Alabama, USA, were obtained by hydrodistillation and analyzed by GC-MS. A total of 69 compounds were identified in the J. regia oil, accounting for 99.0% of the eluting components of the oil while three different samples of J. nigra were analyzed identifying a total of 99.3%, 99.4% and 99.7% of the oils. The leaf essential oil of J. regia was dominated by the aromatic compounds eugenol (27.5%) and methyl salicylate (16.2%), and the sesquiterpenes germacrene D (21.4%) and (E)-beta-farnesene (8.2%). The essential oils from three different samples of. J. nigra contained (E)-caryophyllene (17.3%-20.4%) and germacrene D (7.1%-22.5%) with smaller amounts of juglone (1.0%-8.8%), alpha-hydrojuglone (1.0-9.5%), and delta-cadinene (3.8%-8.7%). J. regia leaf oil, devoid of juglone, showed allelopathic activity, while J. nigra leaf oil was less phytotoxic. The presence of eugenol and methyl salicylate in the leaves of J. regia are consistent with the traditional uses of this plant to treat toothache, rheumatism, and fungal infections.