Naphthyridinomycin complex, a major component thereof called naphthyridinomycin A and a minor component thereof called naphthyridinomycin B are disclosed. These antibiotic substances exhibit antibacterial activity. The substances are producible by culturing a microorganism of the species Streptomyces in an aqueous nutrient medium under submerged aerobic fermentation conditions. Methods for their preparation and use are included.