A number of polyether antibiotics containing two spiroketal functions in their molecular structure are known, including dianemycin, lenoremycin (A-I30A), and leuseramycin (TM-531A), which constitute the lb(2) type in the recent classification scheme and are 3-glycosides due to the presence of 4-O-methylamicetose. This report describes the first example of a polyether antibiotic containing two spiroketals but lacking 4-O-methylamicetose or any other sugar moiety, antibiotic X-14931A, which is formally the 19-deoxyaglycone of dianemycin. Its structure was determined by X-ray analysis of the silver salt hydrate. X-14931A was isolated from the fermentation broth of Streptomyces sp. X-14931 via EtOAc extraction, solvent partitioning, and silica gel chromatography, yielding its sodium salt, free acid, and silver salt, with physical and chemical properties (melting point, specific rotation, elemental analysis) characterized. It demonstrates in vitro bioactivity against Gram-positive microorganisms (e.g., Streptococcus faecium, Staphylococcus aureus), molds, and yeasts (MIC 0.24-62.5 μg/ml), is active against mixed Eimeria infection in chickens at 50 mg/g in feed, and exhibits activity in the rumen growth promotant test. After the study, a US patent for antibiotic 53,607 claimed an identical structure but with inconsistent microanalytical data.