PROBLEM TO BE SOLVED: To produce the subject material, producible in a simple production process at a low cost, capable of manifesting excellent biocompatibility and biodegradability (environmental protection properties) and useful as a paper diaper, a cosmetic, a soil water holding agent or the like by including a specific protein as a principal component therein.
SOLUTION: This water absorbing and water holding material contains (A) a sulfated silk protein as a principal component. The material is obtained by treating (X) a silk protein, e.g. fibroin with (Z2) a sulfating agent such as chlorosulfuric acid or fuming sulfuric acid in (Z1) a reactional solvent such as pyridine (by dispersing, e.g. the protein X in the solvent Z1, providing a dispersion of the protein X and adding the resultant dispersion into a previously prepared mixture of Z2 and Z1), neutralizing the obtained reactional mixture with (Z3) an aqueous solution of a basic compound and recovering the material therefrom.