Triple helical lentinan, beta-(1-->3)-D-glucan from Lentinus edodes, was denatured in dimethlysulfoxide (DMSO) into single random coils. The DMSO solutions of randomly coiled lentinan were diluted with pure water to different w(H) (the weight fraction of water in the mixed solvent), and their specific optical rotation [alpha](D), reduced viscosity (Ineta(r))/c, and hydrodynamic radius R-h were investigated as a function of w(H) and storage time t. With an increase of w(H) from 0.1 to 0.2, [alpha](D) increased sharply, suggesting that transition of conformation of the macromolecules has occurred. When w(H) was lower than 0.1, (Ineta(r))/c of lentinan in water-diluted DMSO exhibited the almost same value as that in pure DMSO and changed hardly with increasing t. Interestingly, (lneta(r))/c decreased to reach a minimum with a further increase of w(H) from 0.1 to 0.25 and then increased with a continuous increase of w(H) from 0.25 to 0.5. Both (Ineta(r))/c and R-h of the denatured lentinan in water-diluted DMSO with w(H) of similar to0.25 both exhibited a minimum, indicating that collapsed coil chains have occurred. All of the experimental findings revealed that the behaviours of lentinan in water-diluted DMSO solution with w(H) < 0.1 were consistent with that in good solvent, DMSO. When w(H) = 0.25, the quality of the mixed solvents became worse, and the dominant intramacromolecular hydrogen-bond interaction enhanced, leading to minimum of viscosity and size of the chains as a result of the collapsed coils. When w(H) >0.25, the quality of the mixture weakens further, and the intermolecular hydrogen-bond interaction enhanced and was dominant, leading to aggregation of the collapsed chains.