The chemical composition of the essential oil from the aerial parts of Chromolaena odorata, collected from Phitsanulok, Thailand was analyzed by means of GC-(FID) and GC-MS. Twenty-two constituents were identified. The major components were pregeijerene (17.6%), germacrene D (11.1%), alpha-pinene (8.4%), beta-caryophyllene (7.3%), vestitenone (6.5%), beta-pinene (5.6%), delta-cadinene (4.9%), geijerene (3.1%), bulnesol (2.9%), and trans-ocimene (2.2%).