Mercapto amino acid,owing to the presenee of the reactive sulfhydryl group could not he prepared by the general methods for the synthesis o1.a-cmino acids. Thus,}lthou5h a number of disulfide of mercapto amino acid e.g. peatocys in and hexocystin,have been reported by da Vigneaud^[10,11], amino acids with a free mercapio group are rare in the literature. One of us (Yuen) has introduced a method in the preparation of e-m:rcapto-αa-aminocaproic acid tin basis of the oxalie ester synthesis^[1]