PROBLEM TO BE SOLVED: To provide a method for treating a distilled liquor waste liquid at a low cost and producing an excellent plant-modifying composition at the same time, and to provide a plant-modifying composition which is produced by the method and has an improved effect.SOLUTION: There is provided a production method of a plant-modifying composition, which comprises steps of: providing a lactic acid bacterium-liquid containing lactic acid bacteria; providing a mixture containing a distilled liquor waste liquid, a carbon source, and the lactic acid bacterium-liquid; fermenting the mixture under conditions suitable for proliferation of the lactic acid bacteria to obtain a fermented liquid; and removing fibers from the fermented liquid and providing a plant-modifying composition.SELECTED DRAWING: None【課題】低コストで蒸留酒廃液を処理すると同時に、優れた植物改良組成物を製造するための方法や、同方法により製造され、かつ、効果が改善された植物改良組成物を提供すること。【解決手段】本発明は、植物改良組成物の製造方法であって、乳酸菌を含む乳酸菌液を提供する工程と、蒸留酒廃液、炭素源、および該乳酸菌液を含む混合液を提供する工程と、該乳酸菌の増殖に適した条件下で該混合液を発酵させて、発酵液を得る工程と、該発酵液から繊維を除去して植物改良組成物を提供する工程とを包含する製造方法を提供する。【選択図】なし