Two new compounds, nanaomycin F and G, were isolated by physicochemical screening method from cultured broth of Streptomyces rosa subsp. notoensis OS-3966, which is known to produce nanaomycin A, B, C, D, and E. Nanaomycin F is a new nanaomycin analog, a 4a-hydroxyl analog of nanaomycin B. Nanaomycin G has a unique skeleton with 1-indanone infused with a tetrahydropyran ring. Nanaomycin A possesses broad antimicrobial activity but nanaomycin F and G demonstrated no bioactivity against all bacteria and fungi tested in this study. In addition, in both nanaomycin F and G, the production of superoxide radicals was majorly decreased in comparison to nanaomycin A. It was considered that the antimicrobial properties were lost as a result of the decrease in production of the superoxide radicals. (C) 2015, The Society for Biotechnology, Japan. All rights reserved.