In the course of screening actinomycetes for novel antimicrobial substances, a new strain of Streptomyces sp. was found to produce a new polyether antibiotic, CP-96,797 (1). This paper describes the isolation, properties and structure of 1, which is related to K-41A. The 100-liter fermentation of Streptomyces sp. ATCC 55028 and isolation of crude 1-Na as an ethyl acetate soluble oil were carried out, followed by purification via HPLC on a silica gel column using methylene chloride - ethanol (3 : 2). The free acid form of 1 was prepared by shaking a chloroform solution of 1-Na with hydrochloric acid at pH 2. Physico-chemical properties of 1 and 1-Na (e.g., MP, [α]₅₄₆, solubility) were given in Table 1. Spectroscopic data were consistent with C₄₇H₈₀O₁₇ for free acid 1 and C₄₇H₇₉O₁₇Na for sodium salt 1-Na, with positive FAB-MS detecting diagnostic cationized molecules m/z 939 (M+Na)⁺ and 961 (M+2Na-H)⁺ for 1-Na. Furthermore, 13C, ¹H and DEPT NMR data for 1-Na revealed groups including CH₃, CH₂, CH, CH₃O, O-CH, C-O, O-CH-O, and comparisons with K-41A showed structural relationships.