In our previous paper, we showed similarities in antibiotic biosynthesis and antibiotic resistance between Streptomyces tenjimariensis and Micromonospora olivasterospora that produce istamycins (IS's) and fortimicins (FT's), respectively. It was demonstrated that these organisms were capable of converting biosynthetic intermediates derived from each other to antibiotic substances including a new one. In this paper, we report the structure determination and some physicochemical properties of the new antibiotic (named 1-epidactimicin; EDC) isolated from the FT-B supplemented cultured broth of S. tenjimariensis U41, a blocked mutant of IS-biosynthesis, as well as its antibiotic activity. Antibiotics accumulated by S. tenjimariensis U41 incubated in a fermentation medium supplemented with FT-B were isolated and purified, with two active peak fractions (III and IV) being further processed. The 13C NMR chemical shifts and 400MHz 1H NMR parameters of EDC were determined, and its antimicrobial spectrum was also presented.