Chromolaena odorata (L.) King and Robinson, an invasive species of the Asteraceae Family, is a weedy shrub native to the warm Central and South America but has successfully invaded other regions of the world including the Philippine islands. Its invasiveness is partly associated with allelopathic properties, but phytotoxic and antimitotic potentials of C. odorata from the Philippines have not been studied. Ethanol and aqueous crude extracts of C. odorata leaves were tested on seed germination and seedling growth of Lycopersicum esculentum (tomato). The lowest concentration level that significantly inhibited germination and seedling growth in L. esculentum was lower (0.5%) for ethanol crude extract than that (5.0%) of aqueous crude extract. The 0.5% ethanol crude extract also reduced the mitotic index in Allium cepa (onion) root tips. Column chromatographic elution of ethanol crude extract yielded 11 fractions, each of which was subjected to bioassay. Only fractions 4 and 5 inhibited seed germination in L. esculentum at 25% concentration. Phytochemical screening of fractions 4 and 5 are positive for the presence of alkaloids and steroids that may have caused the inhibition of seed germination and seedling growth in L. esculentum, and the reduction of the mitotic index in A. cepa root tips. These findings may help explain the wide invasion of C. odorata in the Zamboanga Peninsula.