The 12 marine cyanobacterial species were isolated from Adirampattinam coast, and cultured in ASN Ⅲ media. Based on their growth characteristic, three species namely Oscillatoria sp., Phormidium sp. And Lyngbya majuscule were selected for antibacterial assay against the human pathogenic bacteria such as Streptococcus mutants, Staphylococcus aureus, Pseudomonas aeruginosa, Bacillus subtilis and Klebsiella pneumoniae. The experiments for the inhibition activity onhuman pathogenic bacterial strains were carried out at different concentration levels (250, 500 and 750μg mL^(-1)) of crude extract of 3 species of Cyanobacteria. Among the 3 cyanobacterial species extracts, Oscillatoria sp. showed the maximum inhibition (20 nm) against pathogen strain compared to other species and the minimum inhibition activity (7.2 nm) was observed in the extract of L. majuscule. The species Oscillatoria showed maximum zone of inhibition against pathogenic bacterial active revealed the potential of cyanobacterial extract.