Cyanobacteria are a rich source of biologically active substances with antibacterial, antiviral, immunosuppressive or immunostimulatory activity, which are used mainly in the pharmaceutical industry. Two types of extracts (methanol-water and methanol-chlorophorm) were prepared from 14 cyanobacterial strains of the genera Phormidium, Microcoleus and Phormidesmis, and were evaluated for antimicrobial properties against two bacterial strains – Bacillus cereus (Gram-positive bacterium) and Pseudomonas aeruginosa (Gram-negative bacterium). Only the polar extracts demonstrated antibacterial activity. Five of cyanobacterial strains (Phormidium autumnale PACC 5511, Phormidium autumnale PACC 5527, Phormidium autumnale PACC 5529, Phormidium papyraceum PACC 8600 and Microcoleus vaginatus CCALA 152) showed antimicrobial effects against Bacillus cereus. Maximum antibacterial activity against this Gram-positive bacterium with a zone of inhibition of 30±1 mm showed Phormidium autumnale PACC 5527. Also, 12 from all 14 studed cyanobacteria inhibited the growth of Pseudomonas aeruginosa. Maximum antibacterial activity against this Gram-negative bacterium showed Phormidium autumnale PACC 5517 with a zone of inhibition of 31 mm. Cyanobacterial strains exhibiting antibacterial activity against Bacilus cereus suppressed also the growth of Pseudomonas aruginosa. These extracts have a broad-spectrum of action against both Gram-positive and Gram-negative bacteria. Our data confirm the presence of promising antibacterial compounds that could be derived from selected cyanobacteria.