A polysaccharide designated fl-D-glucan A, extracted from the plant Auricularia auricula-judae with 70% ethanol and then with aq 1% NaCI, has a backbone chain of (1 --> 3)-fl-D-glucose residues, two out of three glucose residues being substituted at 0-6 by single glucosyl groups [1]. Measurements by light scattering, membrane osmometry, and viscometry show that the fl-D-glucan A dissolves as a single-stranded helical structure in water and as a semi-flexible chain in dimethyl sulfoxide (Me2SO) [2]. Analysis of the data in terms of Yamakawa-Fujii-Yoshizak theory yielded 1030 ___ 100 nm -I, 90 + 20 nm, 1.3 ___ 0.3 nm, and 0.26 __+ 0.03 nm for the molar mass per unit contour length ML, persistence length q, diameter d, and contour length h per main-chain glucose residue of glucan A in water, and 19 + 5 nm for q and 1.3 ___ 0.3 nm for d in Me2SO , which was considered to indicate semi-flexibility. In this work, intrinsic viscosities [~/], number-average molecular weights Mn, and second virial coefficients A 2 of the glucan A were investigated as functions of wMe2s 0 (the mass fraction of Me2SO in water-Me2SO mixtures). The Mn value is relative to the total number of molecules present, and so it can reflect changes in single-or multiple-stranded structure.