Means are offered for making effective use of organic wastes and waste oils from the food industry, food processing industry, livestock industry and the like. Furthermore, a method for treating wastes without generating any malodorous fumes, and a feed composition with high nutritional value, promoting the health and fattening of livestock, are offered. An organic raw material such as raw garbage, livestock manure, seafood processing industry waste, distillatory effluents or the like is immersed in a heated oil and extracted to perform an oil treatment, then added to koji and allowed to ferment. The fermentation by the koji mold causes the oil content to fall to a predetermined amount, while the heat of fermentation is used to reduce the water content of organic raw materials, thus producing a koji feed composition.