PURPOSE: To provide a method for poducing L,L-propanediaminedisuccinic acids (EDDS), excellent in biodegradability in an easy process having good reproducibility in high yield and purity.

CONSTITUTION: This method for producing an alkali metal salt of L,L- propanediaminedisuccinic acids(PDDSs) comprises carrying out addition reaction of acrolein with L-aspartic acid under alkaline conditions, further condensing the addition product with one molecular L-aspartic acid and reducing the resultant Schiff base by catalytic hydrogenation in the presence of a catalyst. The method for producing L,L-PDDSs comprises reducing the resultant Schiff base by catalytic hydrogenation in the presence of a catalyst and then depositing the L,L-PDDS with an acid to crystalize L,L-PDDS. Another method for producing L,L-PDDSs comprise reducing the resultant Schiff base by catalytic hydrogenation in the presence of a catalyst and then carrying out deposition and crystallization with a mineral acid. Another method for producing alkali metal salt of L,L-PDDSs comprises reducing the resultant Schiff base with a metal hydride.