Changes of the structure and physical properties of polysaccharide aqueous solutions by annealing are discussed based on the experimental results of viscoelastic measurements and thermal analysis. In the annealing process of polysaccharide aqueous solutions, dynamic modulus increased as functions of annealing time and temperature suggesting the change of molecular association. It was found that the solution annealed in the sol state tends to form hydrogels. Furthermore it was shown that the amount of non-freezing water in the system is closely related to the molecular association of polysaccharides and gelation characteristics. In this dtudy, the structural change of polysaccharides, such as xanthan gum and hyaluronan, in the annealing process is discussed based on the experimental results.