An improved LC method is described for the separation of doxycycline and its impurities. The separation of 2-acetyl-2-decarboxamidodoxycycline from the main peak doxycycline is much better than that obtained with official phormacopoeia methods. The method is robust and shows good selectivity, repeatability, linearity and sensitivity. Eight commercial samples were examined using the method developed. The method uses an XTerra RP-18, 5 mum (25 cm x 4.6 mm I. D.) column kept at a temperature of 35 degreesC. UV detection is performed at 280 nm. The mobile phase consists of acetonitrile -0.2 M tetrabutylammonium hydrogen sulphate pH 7.0 - 0.3 M ethylenediaminetetraocetate pH 7.0 - water (130:350:350:170, v/v/v/v).