Abstract: Microbial corrosion is recognized as one of the major problem in various fields during favorable environment for biological growth that causes fouling and corrosion problems. In the present study, an attempt has been made to evaluate the biocidal and corrosion inhibitory effect of three seaweed extracts such as Turbinaria, Jania and Gelidiella on mild steel. Among the three seaweed extracts Turbinaria ornate showed a highest biocidal effect (84%) followed by Gelidiella acerosa (73%) and Jania adhaerens (71%) mainly this biocidal efficiency was revealed to be concentration dependent. The antibacterial activity of the seaweed extracts were tested against Bacillus sp., Micrococcus sp., (Gram+ve, g+ve) Klebsiella sp., Pseudomonas sp., (Gram-ve, g-ve). All the three seaweeds showed superior antibacterial activity. Pseudomonas was found to relatively resistant to all the three seaweeds. The seaweed extracts found to inhibit corrosion of mild steel for both seawater and 0.5 N HCl. Whenever, concentration of seaweed extracts increased the corrosion inhibition efficiency also been increased. While, 90.7% corrosion inhibition was achieved seawater added with Turbinaria extracts. Relatively Gelidiella sp., showed least inhibitory effect in seawater. Moreover, in seawater the Turbinaria extracts showed peak corrosion inhibitory activity range was 76.49% in acid medium. Meanwhile, minimum and maximum antifouling activity also observed on seaweed extracts such as Jania adhaerens and Gelidiella acerosa. The results indicated that marine seaweed could provide an important source of natural antibacterial, anti fouling as well as anticorrosion activity possessed bioactive compounds and that the interaction between marine microbial floras cannot easily be generated.