Abstract Several cobalt(III) complexes of the [Co(apS or apSe)(N4)]2+ type were prepared, where apS and apSe denote chiral 1-amino-2-propanethiolate-N,S and 1-amino-2-propaneselenolate-N,Se ligands, respectively, and N4 is (en=ethylenediamine)2, (R-chxn=(R,R)-1,2-cyclohexanediamine)2, or tren=tris(2-aminoethyl)amine. Their circular dichroism (CD) spectra were compared with one another and with those of complexes containing such ligands as achiral 2-aminoethanethiolate-N,S, 2-aminoethaneselenolate-N,Se or chiral 1-amino-2-propanolate-N,O (apO). The vicinal CD curves of S-apS obtained from CD spectra of the en and R-chxn complexes are similar and very large in magnitude in the d-d absorption band region. These curves are very similar to the CD spectrum of [Co(S-apO)(NH3)4]2+. The vicinal CD curve of S-apSe shows a similar pattern, but the magnitude is smaller than those of the S-apS and S-apO ligands. The vicinal effect of the protonated S-apSH ligand is much smaller compared with that of its conjugate base (S-apS) ligand. The tren complexes of S-apS and S-apSe exhibit CD spectra fairly different from the vicinal CD curves of the respective ligands in the d-d absorption band region.