An ion-pair reversed phase high performance liquid chromatographic method with UV detection was developed for the determination of azithromycin using sodium heptanesulfonate as an ion-pair reagent. The mobile phase consisted of a mixture of ammonium dihydrogen phosphate (0.045 M, pH 3.0 adjusted by phosphoric acid):acetonitrile 47:15 (v/v) and the concentration of sodium heptanesulfonate in the aqueous phase was 0.002 M. UV detection was performed at 210 nm. The chromatographic column was Dikma Technologies Diamonsil C18 column, 5 microm 150 mm x 4.6 mm, which was maintained at 25 degrees C. Applying the method to a stability study of azithromycin eye drops, it was found that the related substance could be detected and the profile of the AZM peak was symmetrical and the column efficiency was high. Accordingly, it is suitable for the routine analysis and stability testing of azithromycin preparations.