Two complexes of fac(NH3)-[Co(L)(NH3)3]+ type (where L denotes (R)-2-(carboxymethylthio)propionate and (R)-2-(2-carboxymethylthio)propionate) were newly prepared and separated into two isomers, R(S), R(C) and S(S), R(C), by column chromatography. The absolute configurations of the isomers are suggested on the basis of the 13C NMR spectra.