Essential oils obtained from hydrodistillation of three medicinal plants grown in Vietnam were analyzed by gas chromatography (GC) and gas chromatography/mass spectrometry (GC-MS). The monoterpene hydrocarbons, α-pinene (50.2%), β-pinene (23.6%) and limonene (5.3%) were the most abundant constituents of the rhizome oil of Zingiber collinsii Mood & Theilade (Zingiberaceae). The main compounds of the stem oil of Croton kongensis Gagnep., (Euphorbiaceae) were benzyl benzoate (12.7%), β-selinene (9.8%), bulnesol (8.0%) and 5,6,7,8-tetrahydroquinoxaline (7.4%). The leaf oil of Goniothalamus albiflous Ban., consisted mainly of α-pinene (26.2%), caryophyllene oxide (10.6%) and 1,8-cineole (9.7%). The composition of the oils of Zingiber collinsii and Croton kongensis was being reported for the first time.