Abstract: The present paper describes a quantitative determination method oftetracyclines by reversed phase high performance liquid chromatography. The method used a Waters 10 C₁₈ 4. 6 nm ID×250 nm reversed phase column, witha mobile phase composed of 14% acetonitrile-3% dimethylformamide-83% water con-tining 0.02 mol/L citric acid (pH≈2.5), the detector wavelength was set at 350 nm, andthe flow rate was maintained at 1.0 ml/min. Demethylchlortetracycline, epi-demethylchlortetracycline, demethyltetracycline, epi-demethyltetracycline, tetracycline, epi-tetracycline,chlortetracycline and epi-chlortetracycline can be separated highly efficiently. Thetetracyclines and their anhydro-products can be separated on the same column with 15%acetonitrile-15% dimethylformamide-70% O. 02 mol/L citric acid as the mobile phase,and detected at UV 270 nm.