PROBLEM TO BE SOLVED: To provide a method of producing raw material of an additive for feeding stuff which is used as raw material of a feed additive, has a lot of amino acids and can stably culture minute animals.SOLUTION: A method of producing raw material of an additive for feeding stuff comprises: a first biological treatment step of introducing organic waste water containing 40 wt.% or more of protein to a first biological treatment tank and performing aerobic biological treatment by using bacteria, thereby obtaining a first biological treatment liquid containing dispersing bacteria； a second biological treatment step of introducing the first biological treatment liquid to a second biological treatment tank and performing activated sludge treatment, thereby obtaining a second biological treatment liquid； a solid-liquid separation step of performing solid-liquid separation of the second biological treatment liquid into separated sludge and separated water； and a sludge separation step of taking out at least part of sludge in the second biological treatment tank and/or part of the separated sludge, thereby obtaining raw material of an additive for feeding stuff.【課題】飼料添加物の原料として用いられる、アミノ酸を多く含む微小動物を安定して培養することができる飼料用添加物の原料の生産方法を提供する。【解決手段】たんぱく質を４０ｗｔ％以上含む有機性排水を、第１生物処理槽に導入して細菌により好気性生物処理して分散性細菌を含む第１生物処理液を得る第１生物処理工程と、第１生物処理液を第２生物処理槽に導入して活性汚泥処理して第２生物処理液を得る第２生物処理工程と、第２生物処理液を分離汚泥と分離水とに固液分離する固液分離工程と、第２生物処理槽の槽内汚泥の一部及び／又は該分離汚泥の少なくとも一部を取り出して飼料用添加物の原料として得る汚泥分離工程とを有する飼料用添加物の原料の生産方法。【選択図】図１
