To provide a method for preparing a fatty acid silber salt excellent in an antifogging power when used as thermally developable photosensitive material, and excellent in the aged antifogging power, and to prepare thermally developable photosensitive materials of good quality using the fatty acid silber salt.

This fatty acid silber salt is prepared by the following steps: (1) preparation both (A) an aqueous solution or a mixed solution of water with an organic solvent, each containing silver ions and having a pH value ≤6 and of (B) an aqueous solution of a fatty acid alkali metal salt or a mixed solution of the aqueous solution with an organic solvent; (2) adding the solution B to the solution A while stirring the solution A and mixing them to form the fatty acid silber salt.