The effects of aqueous extract from the sheath, leaf and root of two rice materials (HG1 and HG2) on the growth of barnyardgrass were studied. The results showed that HG1 had strong allelopathic effects on the growth of roots and seedling of barnyardgrass, while HG2 only on the growth of roots. Leaf and sheath extracts had more significant inhibitory effects on the growth of barnyardgrass than root extract and distilled water. Root growth of barnyardgrass was significantly inhibited by aqueous extract of root, sheath and leaf of rice. The inhibiting effects on barnyardgrass were negatively relevant to barnyardgrass density, which might be induced by the decreasing amount of individual-absorbing allelochemical.