It is a key of the breeding of ailelopathic rice cultivars to evaluate and screen few accessions with ailelopathic traits from numerous rice accessions and individual plants. Rice varieties and individual plants with ailelopathic traits demonstrated their ailelopathic effects by producing and releasing specific secondary metabolites into environment. Therefore, using specific secondary metabolites as markers, the ailelopathic potentials of rice varieties and individual plants could be evaluated by HPLC. The ailelopathic potentials of 3000 rice accessions and some individual plants of F3 and F4 were evaluated by this method in 1 a. If these accessions and plants were evaluated by the traditional method in the field, it would take more than 10 a, furthermore, the breeding process of ailelopathic rice cultivars would be directed and monitored by this method. Isolation and structural identification of specific secondary metabolites was done by LC/MS coupling 1H and 13C NMR. It revealed that allelochemicals o It is a key of the breeding of ailelopathic rice cultivars to evaluate and screen few accessions with ailelopathic traits from numerous rice accessions and individual plants. The use of specific secondary metabolites as markers, the ailelopathic potentials of rice varieties and individual plants could be evaluated by HPLC. The ailelopathic potentials of 3000 rice accessions and some individual plants of F3 and F4 were evaluated by this method in 1 a. accessions and plants were evaluated by the traditional method in the field, it would take more than 10 a, furthermore, the breeding process of ailelopathic rice cultivars would be directed and monitored by this method. Isolation and structural identification of specific secondary metabolites was done by LC / MS coupling 1H and 13C NMR. It revealed tha t allelochemicals o