Conyza canadensis(L.)Cronq.is a widespread weed species forming dense populations in most regions of China.In the present study,Petri dish bioassays with aqueous extracts of the aboveground parts and roots of C.canadensis at three concentrations(0.05,0.1 and 0.2 g/ml)were undertaken to investigate the autotoxic effects of C.canadensis to itself,and possible effects on three dominant native weed species,Digitaria sanguinalis,Plantago asiatica and Youngia japonica.The results showed that seed germination and shoot length of three native species were signif icantly inhibited by aqueous extracts of C.canadensis at almost all concentrations.This inhibitory effect generally increased with increasing extract concentration and was more prominent with application of extract of aboveground part than root extract.However,the seed germinat ion and shoot length of C.canadensis itself was not signif icantly affected by the same extracts at all concentrations.These results demonstrated that C.canadensis can successfully inhibit the performance of some native plants with no autotoxic effects,suggesting the potential inhibitory effects of allelopathic compounds produced by tissue of C.canadensis may contribute to its invasive success in its invaded ranges.