Abstract Curdlan-type polysaccharide was found to form a thermo-reversible gel in DMSO with the addition of water. The sol–gel transition was also reversible with respect to mole fraction of DMSO. Drastic changes in light scattering intensity, viscosity and optical rotation of the polysaccharide in DMSO with the addition of water were observed around the sol–gel transition point. The gelation mechanism of the polysaccharide in DMSO-H2O mixed solvents is discussed.