Abstract: To study the development and utilization of Tithonia diversifolia and Ageratum conyzoides, constituents of essential oils extracted by simultaneous distillation and extraction (SDE) from these two plants were analyzed qualitatively and quantitatively by gas chromatography/ mass spectrometry (GC-MS). Results showed that 66 compounds were identified. The common components were 3-Hexen-1-ol, α-Pinene, Camphene, β-Pinene, α-Terpinene, Limonene, Terpinolene, α-Copaene, β-Bourbonene, β-Caryophyllene, Precocene I, Germacrene-D, Cubenol, Elemol, Nerolidol, Germacrene D-4-ol, Caryophyllene oxide, Cubenol and Tau Cadinol. Many constituents of essential oils from these 2 invasive plants could have a high value when used as medicines.