A new antibiotic SF-1771 substance is produced by cultivating a new strain, Streptomyces toyocaensis SF-1771, in a liquid culture medium under aerobic conditions. This antibiotic may be isolated from the fermentation broth by treating the broth filtrate with a synthetic adsorbent resin for adsorption of the active compound and eluting the resin with an aqueous alcohol or aqueous acetone, followed by chromatographic purification. SF-1771 substance is a copper-containing antibiotic which shows antibacterial activity against Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis. Removal of the copper component from SF-1771 substance by treatment with hydrogen sulfide, an alkali metal sulfide or a copper-chelating agent gives SF-1771-B substance containing no copper component which shows antibacterial activity as high as but a toxicity lower than SF-1771 substance.