To provide a new method for producing melamine polyphosphate, by which the melamine polyphosphate having a sufficiently high decomposition temperature, not accompany its coloration, does not cause a problem that electroconductivity is increased, when absorbing moisture, and has a high polymerization degree can easily be produced.

This method for producing the high polymerization degree melamine polyphosphate comprises calcining a solid raw material composition comprising melamine, ammonium phosphate, and urea at 170 to 230°C, preferably 190 to 210°C, and then mainly calcining the calcination product at 270 to 350°C, preferably 290 to 310°C. The ammonium phosphate is preferably dibasic ammonium phosphate.