The purified antimicrobial compound produced by S. platensis was more active against Gram positive, Gram negative bacteria and unicellular fungi, C. albicans. The highest biological activity was recorded against Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis and Aspergillus niger. The results of this investigation proved that cyanobacteria could be a good source for production of antimicrobial agents which could be effective when compared with contemporary antimicrobial compounds.