Abstract: Sample of Crude pyromellitic dianhydride (PMDA) was refluxed with methanol for 2 h, and after cooling the methanol extract was diluted to 100 mL with the same solvent. 20 μL of the solution were introduced into the instrument and content of pyromellitic acid (PMA) was determined under the following chromatographic conditions: ① chromatographic column: Agilent RP18 column (4.6 mm×200 mm, 10 μm); ② mobile phase: mixture of methanol and H3PO4 (0.1+99.9) solution (20+80 by vol.); ③ flow-rate: 1.0 mL·min-1; ④ wavelength of UV-detection: 220 nm. Under the optimized conditions mentioned above, effective separation was achieved among the 4 components present together with the crude PMDA, i.e., the esterification product of PMDA, 1,2,4-benzenetricarboxylic-1,2-anhydride, phthalic acid and pyromellitic acid.