A novel microorganism species belonging to the genus Micromonospora, i.e. Micromonospora sp. A 11725 is found to be capable of producing novel macrolide antibiotics A 11725 I, A 11725 II and A 11725 III. Novel antibiotics A 11725 Ia and A 11725 IIa are also found to be derived by chemical modification of the antibiotics A 11725 I and A 11725 II, respectively. All of these antibiotics or salts thereof exhibit excellent antibacterial and anti-mycoplasmal activities against various microorganisms such as Staphylococcus or Mycoplasma, and therefore useful for various purposes including medicaments.