Abstract: The present invention relates to a method for producing a cellulose-containing powder having a cellulose I crystallinity index of ?20% or more and less than 50%, including adding, to 100 parts by mass of cellulose-containing raw materials having a cellulose I crystallinity index of 10% or more and less than 100%, 0.1 parts by mass or more and 100 parts by mass or less of one or more additives selected from the group consisting of (A) high-molecular weight compounds having acid anhydrides, (B) low-molecular weight compounds having acid anhydrides, and (C) silane coupling agents; and subjecting a mixture to a milling treatment in a dry state. The cellulose-containing powder obtainable by the method of the present invention can be suitably used in various industrial applications such as daily sundries, household electric appliance parts, and automobile parts.