 This paper reports on the synthesis of silver nanoparticles using an aqueous extract of seaweed entremorpha compressa as a reducing and stabilizing agent. The resulting particles were characterized by Fourier transform infrared spectroscopy, x-ray diffraction, scanning electron microscopy, energy dispersive x-ray spectroscopy, and transmission electron microscopy. The particles were found to be spherical in shape with diameters ranging from 4 to 24 nanometers. The particles exhibited strong antibacterial and antifungal activities against both gram-positive and negative bacteria and fungi. Additionally, the particles displayed cytotoxic effects against L-richocytes carcinoma, EACT, cells, with an IC50 value of 95.35G slash ML. These results suggest that the seaweed mediated synthesis of silver nanoparticles may be used for biomedical and pharmaceutical applications. This article was authored by Vijayan Sri Ramkumar, Aravalgam Pagazendi, Kumar Gopalakrishnan, and others.