To remove dihalocarboxylic acids as impurities in an aqueous solution of an amino acid (derivative) and purity to a degree suitable for cosmeticology applications by bringing the aqueous solution into contact with a microorganism producing an enzyme specific to dihalocarboxylic acids (salts).

A microorganism producing an enzyme specific to dihalocarboxylic acids or their salts, e.g. Xanthobacter-autotrophicus ATCC43050 is applied to an aqueous solution containing an amino acid (derivative) having a concentration of ≥20 wt.% in a concentration about 1-100 wt.ppm, preferably about 10-50 wt.ppm. The dihalocarboxylic acids (salts) contained in an aqueous solution of an amino acid (derivative) in a concentration of <1,000 wt.ppm, preferably <200 wt.ppm is removed by hydrolysis, etc.