Abstract: In order to illustrate the mechanism of wheat allelopathy, two strong allelopathic wheat accessions ('115/Qinghai' and '92L89') and one weak allelopathic accession ('Kang10103') were used in a set of hydroponic culture experiments. Roots of Alopecurus aequalis were treated with 0%, 0.2%, 1.0% and 5.0% (v/v) water-based extracts of root tissues of different wheat accessions to determine physiological responses of A. aequalis root to the wheat root extracts. The results showed that extracts significantly inhibited the growth of A. aequalis, with root fresh weight decreasing with increasing extract concentration. Also strong allelopathic accessions had higher inhibitory rates than weak accession. No differences existed among the 3 accessions when extract concentration reached 5.0%. After exposure to extracts, A. aequalis root vigor declined at inhibitory rates of 52.0% 59.6%, 46.5% 55.0% and 27.2% 44.7% respectively for '115/Qinghai', '92L89' and 'Kang10103'. Also no differences were noted between the two strong allelopathic accessions. The contents of soluble protein and methane dicarboxylic aldehyde (MDA) as well as the activities of super-oxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of A. aequalis roots increased significantly after treated with wheat root extracts. The order of the activities of SOD and POD was '115/Qinghai' > '92L89' ≈ 'Kang10103'. The activity of CAT changed significantly with changing concentrations of the extracts, and not with different wheat varieties. The contents of MDA in roots of A. aequalis treated with '115/Qinghai', '92L89' and 'Kang10103' root tissues extracts were respectively 10.9-25.5 times, 5.9-24.2 times and 1.2-6.8 times that of the control. Lipid peroxidation was activated and anti-oxidative flavonoids and phenols were induced in the roots by wheat allelopathy. Thus decreasing root vigor, enhancing protective enzyme activities and synthesizing anti-oxidative substances were promising physiological responses of roots of A. aequalis exposed to wheat allelopathy.