Abstract: High performance liquid chromatography (HPLC) has been widely used in the quantitative analysis of erythromycin 9 oxime, an important intermediate for the synthesis of new erythromycin derivatives. HPLC method is used to analyse the content of erythromycin 9 oxime, and the stability of the method is evaluated. The results show that this method has a good stability and high accuracy. External method is applied, with the following chromatographic conditions: description of column: Nova pak C18, eluent used: V(CH3CN)∶V(0 033 mol/L KH2PO4)=(30∶70), detection wavelength: 205 nm, detection sensitity 0 1AUFS.