During the course of searching new antibiotics effective against fungi, the authors isolated a new Streptomyces strain No. 21-A-2 from the soil at Higashi-Kitazawa, Shibuya-ku, Tokyo. The taxonomic studies of this strain was carried out by one of the authors⁽¹⁾ and this strain was named Streptomyces kitazawaensis nov. sp. This strain produces a substance which shows a specific activity against yeast and fungi especially against Piricularia oryzae. The authors succeeded in obtaining this active substance in crystalline form and this crystal was identified with antimycin A^{2 3 4 5 6 7 8 9 10} according to its physical, chemical and biological properties.

The present paper deals with its isolation, comparison of its physical and chemical properties with Antimycin-A and some biological properties.