A new antibiotic indisocin was isolated from the culture filtrate of actinomycete strain MG323 hF2 which was isolated from the soil sample collected at Shinagawa-ku, Tokyo, Japan. The strain has been classified as Nocardia blackwellii MG323-hF2 by taxonomic studies and assigned as accession number FERMP-6606. In this paper we report the fermentation and isolation procedures, physico-chemical properties, structure determination and biological properties of indisocin (1) and iV-methylindisocin (2) (Fig. 1).