Abstract: The mass spectrometric methods for measuring ~(15)N in plant and soil havebeen reviewed in the present paper. The conventional method is carried outwith three procedures: (1) couverting the labeled nitrogen to ammonium;(2) converting the ammonium to N_2 by oxidation with alkaline sodium hypo-bromite under vacuum condition; (3) determining the isotopic composition ofN_2 by mass spectrometry.