PURPOSE: To provide a method for producing L-aspartic acid-N-monopropionic acid and its alkali metallic salt in a higher yield and purity than those in a conventional method and obtain a biodegradable chelating agent containing at least one thereof as an active component.

CONSTITUTION: This method for producing L-aspartic acid-N-monopropionic acid is to add acrylonitrile to L-aspartic acid under alkaline conditions, further add an alkali metallic hydroxide to the resultant reactional product, hydrolyze the reactional product, subsequently add sulfuric acid thereto and deposit a crystal. Further, the method for producing an alkali metallic salt of the L- aspartic acid-N-monopropionic acid is to react the deposited crystal with an alkali metallic salt or this method for producing a trialkali metallic salt of the L-aspartic acid-N-monopropionic acid is to evaporate the reactional product after the hydrolysis to dryness without adding the sulfuric acid thereto. Furthermore, this biodegradable chelating agent contains at least one of the L-aspartic acid-N-omnopropionic acid and its alkali metallic salt as an active component.