A GC/MS method, using soil incubated with ¹⁵N-NH₄ ⁺and glucose, was developed. The method is efficient in evaluating ¹⁵N incorporation into soil amino sugars and amino acid enantiomers, and in distinguishing between inherent and newly-synthesized amino compounds. As extraneous isotope nitrogen is rapidly assimilated and synthesized into amino compounds in the presence of active substrates, it is feasible to determinate change in peak intensity of the isotope with the aid of the mass spectrum technique. And as there is only one N atom in the molecule of amino sugar and neutral or acidic amino acid, ¹⁵N enrichment degree can be worked out by calculating ratio of the relative intensities of F+1 (isotope peak) and F (parent peak). Since mass spectrum fragment m/z 439 of lysine, a kind of alkaline amino acid, contains two N atoms, ¹⁵N enrichment degree can be calculated based on variation of the relative intensity of m/z 441 (F+2).¹⁵N enrichment degree in the target compound can by expressed as APE, but APE of D-amino acid needs to be calibrated by hydrolysisinduced racemization (HIR%). In general, APE value represents the turnover velocity of amino compounds. So it is a powerful means available for investigating soil nitrogen dynamics.