A method for producing a phosphorylated polysaccharide, characterized by comprising irradiating a solid mixture with microwave, wherein the solid mixture comprises (a) a polysaccharide, preferably at least one component selected from the group consisting of amylose, glucomannan, pullulan, starch, lectin, guar gum and dextran and (b) a phosphoric acid salt compound, preferably at least one component selected from the group consisting of disodium hydrogen phosphate, sodium dihydrogen phosphate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate. According to the production method of the present invention, it is only needed to mix raw material powders together and irradiate the mixture with microwave. Therefore, it is not needed to carry out heating, reduction in a pressure or the like, which is employed in conventional methods, and therefore the cost for the production can be reduced.
