Parthenium hysterophorus Linn. is one of the most aggressive, invasive weeds threatening natural and agricultural ecosystems in Nepal. Leaf feeding beetle, Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), is regarded as a potential candidate for biological control of Parthenium weed. Considering the fact effectiveness of Z. bicolorata against P. hysterophorus was evaluted in Nepal. Z. bicolorata caused 98.25 % defoliation of P. hysterophorus reducing 38.88 % plant height, 27.29 % plant width, 26.25 % root length, 12.33 % leaves, 40.58 % shoot biomass and 36.59 % root biomass in the period of 90 days. The flower production and soil seed bank were reduced by 50.22 % and 40.29 %, respectively. Z. bicolorata was an efficient bio-control agent with a significant negative effect on the vegetative and reproductive performance of the noxious weed P. hysterophorus.