This study was conducted at Research laboratory, Botany Department Amrit Campus, Kathmandu, Tribhuvan University, Nepal, in the year 2015-2016 to investigate the allelopathic effects of compost extract and soil amended with compost invasive weed Parthenium weed on seed germination and seedling growth of two crops Triticum aestivum, Brassica campestris and some common weeds (Ageratum conyzoides, Bidens pilosa, Galinsoga parviflora and Cyperus rotundus). Parthenium hysterophorus was collected before flowering and matured seeds of Bidens pilosa, Ageratum conyzoides, Galinsoga parviflora and Cyperus rotundus were collected from different sites around Kathmandu valley like Kirtipur and Bhaktapur areas. The compost extract of Parthenium of different concentration (control, 1, 2.5, 5 and 10%) and Parthenium compost (control, 10, 20, 40 and 50 g compost/kg soil) were used to determine its effect on seed germination, shoot and root length of T. aestivum and B. campestris and selected common weed seeds under laboratory condition. The compost extracts of Parthenium caused significant reduction in seed germination, seedling length (shoot and root length) of selected crops and weeds. The selected common weeds showed more reduction in germination and vegetative shoot and root length in comparison to crop plants (B. campestris and T. aestivum) in the soil amended with the compost of Parthenium.