In this study methanolic extracts of four seaweeds belong to Phaeophyceae (Petalonia fascia, Stypocaulon scoparium) and Chlorophyceae (Cladophora prolifera, Codium fragile) that were collected from the Aegean coast of Turkey have been studied for their inhibitor activity against pathogenic microbes (Staphylococcus aureus, Staphylococcus epidermidis, Salmonella typhimurium, Enterobacter aerogenes, Escherichia coli, Enterococcus faecalis and Escherichia coli O157:H7), in vitro. Against the extracts of all the tested marine algae, S. aureus was the most sensitive bacteria since it was inhibited by most of the extracts. On the other hand, the highest inhibitor activity was shown to Enterobacter faecalis by the extract of Codium fragile. Whereas, the growth of Salmonella typhimurium and Enterobacter aerogenes were not inhibited by any of the extracts