Phototropism is one of the common growth responses of plants tounilateral irradiation. Went proposed that phototropism is caused by a lateralgradient of growth-promoting auxin in the bending organ (Cholodny-Went the-ory). Recently， Bruinsma found that the shaded half did not contain more auxinthan the illuminated half. We have been investigating the relationship betweenplant growth inhibitors and growth inhibition by light in plant， and have succeededin isolation some light-induced growth inhibitors and these precursors related tophototropism.  In this study we describe herein the isolation of the light-induced growthinhibitors from light-grown buckwheat seedlings. The EtOAc fraction of the light-grown seedlings caused considerable growth inhibition， and this findings suggestthat the growth inhibition of buckwheat (Fagopyrum esculentum). The growthinhibitors were isolated from light-grown buckwheat shoots and their structureswere determined by spectral data coupled with some reactions as unsaturatedfatty acid hydroperoxides.  They inhibited the elongation of buckwheat shoots under dark conditions. Thepresence of unsaturated fatty acid hydroperoxides in the plant coupled to its effecton growth suggests that they may be involved in light-induced growth inhibitionof buckwheat seedlings.