1. The degree of calcium ion binding to chondroitin sulfate was larger than that of sodium ions. The association of calcium ions with the mucopolysaccharide cannot be ascribed solely to electrostatic forces. 2. No differences in the degree of ion binding of chondroitin sulfate isomers A and C were detectable. 3. The spacing between charged groups of chondroitin sulfate was found to be 0.48 nm, which is consistent with the results of X-ray analysis. 4. The characteristic ratio was large. Therefore, rotation about the backbone bonds is highly restricted.