In recent years, the population of Stellera chamaejasme L. weed is increasing due to degradation of grasslands in northern and western China. It has caused major damage to plant ecosystem but the mechanisms to facilitate the spread of this weed is not clear. We isolated the umbelliferone, as main component from the root exudates of S. chamaejasme grown under laboratory conditions. It was also found in the root zone soil and rhizosphere soil by high performance liquid chromatography (HPLC). In bioassays the umbelliferone drastically inhibited the root growth of seedlings of Elymus dahuricus Turcz., Poa annua L. and Festuca arundinacea, the common forage grasses in meadows. Besides in the degradation experiment, the umbelliferone was completely biodegraded in soil after 2-days, however, the degradation was delayed in sterilized soil. The leaf residues were rich umbelliferone and the content remained higher for longer times. The concentration of umbelliferone in leaves residues was >214 mu g/g and persisted for more than 25 days. Thus the accumulation of umbelliferone as a main allelochemical in root exudates and leaf residue and its decomposition plays major role in allelopathy of S. chamaejasme and help the plant to become a successful invader in the natural plant ecosystem.