Allelopathic activity of Parthenium hysterophorus L. leaf extract of different concentratios were studied on seed germination, seedling growth, fresh wt., r:s ratio, inhibition(-) or stimulation(+),relation elongation of root and shoot and SVI values of Pisum sativum were recorded. In the present study allelopathic activity of leaf extract of different concentrations (5%, 10%, 15%, 25%,50%) were compared to control condition. The higher concentrations of leaf extract reduced the rate of seed germination. In the present study the length of root was inhibited in different treatments (63 to 77%) compared to control condition but the shoot length decreased from 2 to 45% only. The fresh weight of root except for 15% treatment and shoot, r:s ratios and SVI decreased compared to control treatment. The values for relative elongation ratios for root and shoot ranged from 23.09 to 37.67% and 55.54 to 98.34%, respectively.