Cyanobacteria (blue-green algae) are a diverse group of photosynthetic, prokaryotic organisms found in freshwater and marine environments. It produces a variety of secondary metabolites with antibiotic, algicide, cytotoxic, immunosuppressive and enzyme inhibiting activities. Screening of various extracts of cyanobacteria from river for antibacterial activity in different in vitro systems revealed strains with interesting effects. A fresh water cyanabacterium, Oscillatoria limosa is a filamentous algae with trichomes ranging from 2 to 6 ?m in diameter and each cell is 2 ?m in thick. It has proven to be a prolific source of novel, structurally diverse secondary metabolites. The metabolites from various extracts of Oscillatoria limosa from fresh water showed significant antibacterial activity againast Staphylococcus aureus, Salmonella typhimurium, Klebsiella pneumoniae, Pseudomonas aeroginosa, Escherichia coli, Streptococcus pyogenes, Bacillus subtilis. Therefore this text is particularly emphasized the screening of antibacterial activity of Oscillatoria limosa to made a new drug discovery.