Actinomycete strain OM-173, a new soil isolate, was found to produce five nanaomycin-type antibiotics. Antibiotic OM-173 components alpha A, alpha E, alpha B, beta A and beta E were isolated from the fermentation broth of strain OM-173 by solvent extraction, silica gel chromatography and preparative thin-layer chromatography. The components are active against mycoplasmas and to a lesser extent against fungi. Strain OM-173 was identified as a strain of genus Streptomyces and differed apparently from Streptomyces rosa var. notoensis, the nanaomycin-producing strain, in cultural characteristics.