A sustained release preparation of a drug and a method for the sustained release of a drug by using a degradation product of the galactose moiety of galactoxyloglucan as the sustained release ingredient. In the above preparation and method, more particularly, it is intended to achieve the sustained release of a drug by using the reversible heat-responding gelation of a degradation product of the galactose moiety of galactoxyloglucan obtained by partly eliminating the side chain galactose therefrom with the use of an enzyme.
