Flame retardance is a very important property of polymer materials, and red phosphorus is often used as a flame retardant. Because red phosphorus contains a high level of elemental phosphorus, fire-retardant property can be obtained even when polymer materials are very lightly doped with red phosphorus. In material development, quality control, and material acceptance inspection of compound resins, it is important to qualitatively and quantitatively analyze red phosphorus contained. However, the method for analyzing red phosphorus In compound resins is not established yet, because it is very difficult to isolate red phosphorus from resins and also because red phosphorus has a low sensitivity to infrared absorption spectrometry, Raman spectrometry and X-ray diffraction. Pyrolysis-gas chromatography mass spectrometry is used mainly for analyzing organic materials, but because red phosphorus sublimes, the authors found that it shows a characteristic mass spectrum in the pyrolysis-gas chromatography mass spectrometry. This method Is expected to be used for analyzing other products containing red phosphorus.