An antibiotic was isolated from the culture filtrates of Streptomyces lavendulae and named yazumycin. It was isolated from the broth using cation exchange resin and purified by cellulose chromatography. Yazumycin exhibited inhibitory activities against bacteria, especially Gram-negative bacteria suchto mice was shown by intravenous injection of 200 mg/kg. In the course of screening for antibiotics, a new antibiotic was isolated from the fermentation broth of a Streptomyces culture, which resembled to those of Streptomyces lavendulae. This antibiotic, which was named yazumycin, is active against bacteria,especially Xanthomonas oryzae and Xanthomonas citri. In this paper, the taxonomic studies of the producing strain, and the production, isolation, and properties of yazumycin are described.