Optical rotatory dispersion (ORD) and circular dichroism (CD) spectra of several j3-1,4 xylan and cellulose acetates and some of their oligomers were investigated. The CD spectra proved considerably superior in terms of information content and interpretability. Comparison of the xylan and cellulose acetate series which also included partially substituted cellulose acetates showed that the sign of the CD of the C(6) acetyl was negative. Likewise, the combined contribution of C(1) and C(4) to their equatorially substituted acetyls was positive (with C(1) definitely positive) and the combined contribution of C(2),, and C(3),, negative. The solution conformations of both polysaccharide acetates appeared to be random. The CD of white birch xylan acetate which is substituted on the average a t every tenth residue with a 4-0-methyl glucuronic acid substituent, was sensitive to it. The xylan oligomer series also illustrated that CI) may be used to determine the degree of polymerization of these oligomers up to about 20.