The present laboratory experimental study was conducted to evaluate the allelopathic potential of Calotropis gigantea L. On the seed germination, early seedling growth and biochemical parameters of Parthenium hysterophorus L. Aqueous leaf extracts of 0, 25, 50 and 75% w/v of obtained from leaves of Calotropis gigantea. L. Inhibited germination and seedling growth of P.hysterophorus in bioassays conducted in petri plates. In foliar spray bioassay, aqueous leaf extract of 25, 50 and 75 % w/v sprays were given in two times at five day intervals viz., one-week and two–week old Parthenium seedlings. The extracts on potted plants reduced the early seedling growth. Higher concentration of 50 and 75 % leaf extracts was completely inhibited the seedling growth shoot and root biomass and biochemical parameters, viz., protein and chlorophyll content. The present study concludes that the leaves of Calotropis gigantea L. contain allelopathic potentialities of constituents for suppressing the growth of Parthenium hysterophorus

Keywords: Allelopathy, Calotropis gigantea, germination, seedling growth, Parthenium