A series of new antibiotics, Kinamycin A, B, C, and D which are mainly effective against gram-positive bacteria, were extracted with chloroform from the broth filtrate of Streptomyces murayamaensis sp. nov. HATA et OHTANI. Kinamycin C (I), C₂₄H₂₀O₁₀N₂, m/e 496 (M+), was determined to have an 8-hydroxynaphthoquinone skeleton, nitrile, acetoxyl, and tertiary methyl groups from its ultraviolet (UV), infrared (IR), and nuclear magnetic resonance (NMR) spectra, and was further found to have a unique structure of N-C-N from some chemical reactions and X-ray diffraction. Structure relationship among I and other components A, B, and D was assumed to be due to the difference in the number and position of the acetoxyl group from analyses of IR, NMR, and mass spectra of their acetylated compounds. The antimicrobial activity of the four kinamycins increases with the decreasing number of acetoxy group, in the order of kinamycin C, A, D, and B. In addition, some derivatives obtained during structural studies on I were found to have nearly equal or increased antimicrobial activity compared with I and kinamycin D (XI).