To obtain a valuable material utilizable for various fields supporting energy consumption and saving space for the treating equipment without lowering a recycle ratio by modifying a specific crude fibers structural material by performing a treatment by a specific reaction.

This valuable material utilizable for various fields is obtained by modifying (A) a crude fibers structural material comprising water-soluble polysaccharides as residues obtained by performing desalination and/or treating with a basic aqueous solution and/or heat-treating to an organism living in sea water and/or fresh water and a water-insoluble polysaccharides by performing a reaction using an acidic aqueous solution and/or a biological reaction and/or an enzymic reaction. The component A is contained in a leaf, a stalk, a root or an adult leaf, etc., in a foliar bud period to an aged period of Phaeophyceae, Rhodophyceae, Chlorophyceae, Becillariophyceae, Myxophyceae and Cyanophyceae and/or their subspecies. As the polysaccharides, (hemi) cellulose, alginic acid, etc., are exemplified.