Allelopathic effect of aqueous extract of Parthenium hysterophorus (L). were studied on seed germination and seedling emergence of some cultivated crops like Triticum aesticum (L)., Zea mays (L), Sorghum vulgare Pers., Gossipium hirsutum (L) and Glycine max (L). Seed germination of Z. mays was completely inhibited at 2% leaf extract of P. hysterophous and of T. aesticum. It gradually reduced the seed germination up to concentration of 10% while in Sorghum vulgare, it was inhibited at 6%. At 4% aqueous extract, the maximum inhibition occurred in Glycine max and G. hirsutum. The aqueous extract of Parthenium showed strong inhibitory effect on the growth of root and shoot development of crops except T. aesticum.