The effect of extracts from root, stem and leaf of little iron weed (Vernonia cinerea (Linn.) Less) at the ratios of 1:20 and 1:40 (weight of plant: volume of water) on germination and growth of mung been (Vigna radiata (L.)) and rice (Oryza sativa L.) were examined. The results demonstrated that allelopathic potential from leaves and stems extract of little iron weed had more efficiency in inhibiting germination, root length and stem length of mung bean and rice than roots extract. The effect of watering extracts from the leaves, stems and roots of little iron weed at a ratio of 1:20 every 5 days on the growth of marigold (Tagetes patula L.) in pots for a period of 8 weeks. It was found that the extracts from the leaves and stems of little iron weed after watering increased shoot lengths of the marigold plant than the root extract, but the stems are not upright and the leaves are yellow and withered. The extract of the leaves, stems and roots of little iron weed decreased root length of marigold when compared to the control. Therefore, if little iron weed extracts are to be used, they should also be analyzed for the active ingredients contained in the extract.