In the course of our screening for structurally unique secondary metabolites from a microbial metabolite fraction library by spectral database search, a new neoantimycin analog, unantimycin A (1) was discovered and isolated with a known neoantimycin analog, SW-163A (2). The structure of 1 was determined based on extensive spectroscopic methods, including NMR and MS. It had a 3-hydroxybenzoic acid moiety instead of a 2-hydroxy-3 formylaminobenzoic acid moiety and showed moderate cytotoxicity against several cancer cell lines.