To provide a production method of a reduction salting-out keratin fiber which has no trouble at a reduction salting-out process of a keratin-containing material, can produce the reduction salting-out keratin fiber which is stabilized and highly strong at low cost and easily.

In the invented production method of the reduction salting-out keratin, the amount of a surfactant is adjusted 60 wt.% or above and 100 wt.% or below to the mass of a keratin-containing material when a reduction treatment of the keratin-containing material is performed in an aqueous solution which is added with protein modifying agent, surfactant and the third class phosphine compound. Furthermore, the amount of inorganic salt added to the keratin aqueous solution or the aqueous solution of the inorganic salt is adjusted 0.9 M or more and less than a saturated concentration when the inorganic salt is added to the aqueous solution containing the reduction keratin and the keratin is salted out.

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