Abstract: Parthenium hysterophorus L.is an aggressive herbaceous weed from the Asteraceae family.It invades disturbed environments of different nutrient levels such as arable land,waste land,and roadside.The reproductive adaptability of this weed to different nitrogen and phosphorus levels was studied.The results showed that SPAD value,branch and inflorescence number,total biomass,flower mass and its ratio,and seed set increased with increasing nitrogen levels.While height and 1000-seed weight increased with increasing phosphorus levels,other parameters showed no increase.This weed acclimated to a wide range of nitrogen environments through increased seed production,which was achieved by enhancing branch and inflorescence number,flower mass and its ratio, as well as seed set,and to phosphorous rich environments through improved seed quality.The addition of nitrogen and phosphorus in soil could,therefore,promote the reproductive ability of Parthenium hysterophorus,and increase its invasiveness in nitrogen and phosphorus rich environments.