Parthenium is an invasive weed in many parts of the world. In Pakistan, this has now become dominant weed in wastelands, forests and other natural areas and is also becoming a problematic weed in other situations such as irrigated and rain-fed cropping systems, pasture lands. In this preliminary study we investigated the impact of this weed on the soil seed bank of a riparian habitat. The impact of Parthenium weed upon below ground soil seed bank was assessed in the invaded and non-invaded sites along the canal near district Lahore, Pakistan. In the invaded site, the average number of Parthenium weed seeds in the soil was found to be 4,434/m2. The average numbers of seed/m2 and species diversity were lowest in the invaded site while it was highest in weed-free sites. A number of important native plant species such as, Saccharum spontaneum, Eleusine indica and Solanum nigrum were found to be declining in the invaded sites. The long-term presence of Parthenium weed at these sites poses a serious threat to native plant diversity in these habitats.