An organic silver salt composition used for thermally developable photothermographic material is disclosed, comprising at least two organic acids differing in melting point and their silver salts, wherein a silver salt of a lower-melting organic acid account for 10 to 80 mol % of the silver salts and the lower melting organic acid accounting for 0 to 30 mol % of the acids. A method of manufacturing an organic silver salt compositions also disclosed.