The present invention provides a stable isotope-labeled amino acid which is at least one of amino acids constituting a protein and which has at least one of the following labeling patterns: (a) hydrogen atoms except at least one hydrogen atom in one or more methylene groups are deuterated, (b) hydrogen atoms in one of prochiral gem-methyl groups are completely deuterated, (c) hydrogen atoms in prochiral methyl groups are partially deuterated, and (d) all hydrogen atoms except one of them in methyl group are deuterated and hydrogen atoms in the aromatic ring are partially deuterated. With the stable isotope-labeled amino acid, the deuteration of protein can be attained without damaging the NMR sensitivity of remaining hydrogen nucleus and, in addition, the rapid, accurate analysis of NMR spectrum of a high-molecular protein which is beyond the limitation in the prior art and the determination of the stereo-structure can be performed at the same time.