In the course of screening for new antibiotics to overcome resistance encountered in antibacterial chemotherapy, a new phosphoglycolipid antibiotic, designated as AC326-a (1), was isolated from an unidentified Actinomyces. This antibiotic showed potent antibiotic activity against Gram-positive bacteria and was inhibitory to cell wall biosynthesis. Structurally, AC326-a (1) is closely related to moenomycin A (2), the major constituent of the flavomycin® complex which is utilized in animal nutrition. In this paper, the production, isolation, biological activity, and structural characterization of the new antibiotic are reported.