Abstract: OBJECTIVE To establish a method to detect five kinds of known impurities and others unknown impurities in phenylbutazone crude drug and coated tablet. METHODS The HPLC analysis was performed on a Agilent Eclipse XDB-C₁₈(5 μm, 4.6 mm×250 mm)column; the column temperature was 30℃; the mobile phase consisted of ammonium acetate buffer (take ammonium acetate 2.72 g, dissolve 700 ml of water, adjust the pH to 4.1 with glacial acetic acid, add water to 1 000 ml, shake well) and acetonitrile(58:42) at the flow rate of 1.5 mL·min^-1, the detection wavelength was 254 nm, and injection volume was 20 μl. RESULTS Five kinds of impurities were completely separated in 25 min, and good linear relationships of A, B, C, D were obtained in the range of 5-30 μg·ml^-1. good linear relationships of E was obtained in the range of 0.03-0.15 μg·ml^-1, the limit of detection of were respectively 27.86, 28.52, 26.28, 31.96, 0.24 ng; the average recoveries were respectively 98.1%, 99.3%, 97.6%, 97.4%, 95.1% and 96.9%, 97.1%, 96.6%, 96.1%, 94.7%. CONCLUSION The improved method is more sensitive and reproducible, and can be used for quality control of the crude drug and preparation of phenylbutazone efficiently.