A new peptide antibiotic, laspartomycin, was isolated from a Streptomyces designated Streptomyces viridochrontogenes var. komabensis Hamada et Okami. The isolation, purification, physicochemical, and biological properties of the antibiotic were described. Laspartomycin was differentiated from related antibiotic such as aspartocin, amphomycin, glumamycin, zaomycin and crystallomycin by amino acid composition and behavior in paper chromatography. Increase of pathogens resistant to antibiotics has been noted and the need for elimination of this problem is now urgently recognized. Staphylococci often cause stubborn diseases and their resistance to antibiotics are frequently reported. In the authors' laboratory, a search has been conducted for new substances active against resistant staphylococci. Isolation of a new antibiotic named laspartomycin from fermented beer of a streptomyces and its characteristics are reported in this paper.