A fibrous cellulose-containing material capable of significantly improving resin strength and a method of preparation thereof, as well as a fibrous cellulose composite resin excellent in strength. The fibrous cellulose-containing material contains fibrous cellulose which is a carbamate-modified microfiber cellulose having hydroxyl groups, part or all of which are substituted with carbamate groups, and having an average fiber width of not smaller than 0.1 μm, and contains powder that is non-interactive with the fibrous cellulose. The fibrous cellulose composite resin contains fibrous cellulose which is the above-mentioned fibrous cellulose-containing material, and part or all of the resin is powdered resin. The method for preparing a fibrous cellulose-containing material includes adding at least either of powder that is non-interactive with fibrous cellulose and a dispersion thereof, to a dispersion of carbamate-modified microfiber cellulose to obtain a mixed liquid, and removing the dispersion medium from the mixed liquid.