A preparation containing an active form of vitamin D.sub.3 which is stabilized by incorporation of an amino acid that is neither one containing a sulfur atom or an acid amino group in its structure, nor an acidic amino acid, nor a salt of a basic amino acid is disclosed. Examples of said amino acids that may be used as stabilizers of the active form of vitamin D.sub.3 include neutral amino acids such as alanine, valine, proline, phenylalanine, tryptophan, leucine, isoleucine, glycine and serine, and basic amino acids such as lysine, arginine and histidine.