Mycinamicins, novel macrolide antibiotics were obtained from the culture broth of Micromonospora grisseorubida sp. nov. Isolation of five components, mycinamicins I, II, III, IV and V, was accomplished by silica gel adsorption or partition chromatography. Mycinsmicin I and II exhibit a strong UV absorption peak at 218 nm and have a shoulder at 240 nm. Mycinamicin III, IV and V show strong UV absorption peaks at 215 nm and around 280 nm. From their physicochemical and biological properties, the mycinamicins are classified as new macrolide antibiotics.