Optically active poly(gamma-ketosulfide)s containing the (2R,3R)-1,4-dimercapto-2,3-butanediol moiety were reacted with butyraldehyde to obtain the corresponding acetalized derivatives. The optically active low-molecular-weight analogues were also similarly prepared. High- and low-molecular-weight products were characterized by spectroscopic methods and chiroptical techniques. The conformational and stereochemical features of the macromolecules, as compared with the polymeric precursors as well as the low-molecular-weight analogues, are discussed on the basis of nuclear magnetic resonance (n.m.r.) and circular dichroism measurements. In particular, n.m.r. data indicate that the acetalization reaction does not appreciably modify the diastereomeric distribution of the constitutional repeating units and circular dichroism spectra confirm the presence of asymmetric induction on the chromophoric groups, although no evidence is found of structurally ordered conformations having one largely prevailing single chirality.