Background: One of the most active study fields in contemporary materials science is nanotechnology. There have been impressive developments in the field of nanotechnology in recent years, with numerous methodologies developed to synthesize nanoparticles of particular shapes and sizes depending on specific requirements. The number of new uses for nanoparticles and nanomaterials is growing quickly. Secondary metabolites are abundant in ascidians as a kind of chemical defense. Objectives: An attempt has been made to synthesize and characterize silver nanoparticles by using ascidians - Phallusia nigra and Didemnum psammatode and their corrosion inhibitory action. Methods: The nanoparticles were synthesized biologically and characterized by Ultraviolet-Visible (UV-Vis) spectrophotometry, Fourier Transform Infrared (FTIR) Spectroscopy and Scanning Electron Microscopy (SEM). Results: For Phallusia nigra and Didemnum psammatode, the corrosion rates in 24 and 72 hours were recorded as 3.62, 5.05% and 7.32, 11.92 % respectively. Conclusion: The Ag nanoparticles performed efficiently in bringing down the corrosion property of carbon steel in the medium of seawater with ascidian extract.