It is intended to provide a method by which a polysaccharide can be degraded while sustaining the effect of the polysaccharide and a degraded polysaccharide. A method of degrading a polysaccharide which comprises irradiating the polysaccharide with a light in the visible range in the presence of titanium dioxide. In this method, it is preferable that the polysaccharide contains at least one of chondroitin sulfate, heparin and hyaluronic acid. It is also preferable that the energy of the light in the visible range for the irradiation is 1 MJ or more but not more than 20 MJ. Furthermore, it is preferable that titanium dioxide is employed in an amount of 0.1 g or more but not more than 10 g per gram of the polysaccharide as described above.
