The rapid determination method of pyromellitic acid (PMA), pyromellitic monoanhydride (PMMA), or pyromellitic dianhydride (PMDA) was tried by means of NMR spectroscopy. In the spectra of PMA, PMMA, and PMDA mixtures in THF, single sharp signals of these aromatic protons appeared at 8.05, 8.34, and 8.70 ppm, respectively. It was found that PMDA graduately reacted with PMA and formed two equivalent moles of PMMA in THF at a room temperature (Fig.3 and Table 1). PMA, PMMA, and PMDA could be determined by measuring the peak hights of these aromatic proton signals within 20min after dissolving the samples in THF; the formation of PMA did not affect the above determination. The standard deviations of the analytical date of PMA and PMDA, calculated by Youden's method, were 0.59and 0.70, respectively.