[en] Evaluation was made for carbon and nitrogen stable isotope analyses of amino acids which were hydrolyzed from biological samples. Alteration of isotopic compositions during chemical preparations was studied in incorporation with organic solvent, acid hydrolysis, and ion-exchange chromatography. Based on such assessment, analyses of isotope compositions of single amino acids were made for collagen and plant protein. The carbon isotope composition of soybean showed consistent pattern with algal amino acids. Similarity was also found in the intermolecular relationship of δ¹³C and δ¹⁵N between collagen and soybean protein. (author)