A reversed phase high performance liquid chromatographic method for the assay of midecamycin was developed. The method used a Hitachi Gel 3050 column at 50 degrees C and a mobile phase of methanol--0.01 mol/L phosphate buffer solution at pH 5.8 (45:55). The column effluent was monitored Z at 231 nm. SF-837A1, leucomycin A6 and minor components could be separated in less than 15 min. The retention times of SF-837A1 and leucomycin A6 are 7 and 10 min respectively. The method is very simple and rapid.