Greenhouse and laboratory experiments were conducted to determine the allelopathic effects of sunflower on Sinapis arvensis and Setaria viridis with a view to explore its weed seed inhibition potential. Germination of both the weeds was reduced with increasing concentration of sunflower extract and a dose-response relationship was observed. These curves provided information on LC50 and inhibition threshold concentrations of sunflower extracts. Sunflower also inhibited the growth of both the weeds in terms of root and shoot length and seedling dry weight. Inhibition of root growth was greater than that of shoot growth. Similar observations were made when the test weeds were grown in soil amended with different concentrations of sunflower extract. Reduction of chlorophyll content and water loss in the growing seedlings was also observed. The study, therefore, revealed that sunflower exerted an inhibitory effect on the growth and development of both the weeds and can be further explored in future for weed management strategies.