Nanomedicine is an interdisciplinary field, where nanoscience, nanoengineering, and nanotechnology interact with the life sciences. Nanoparticles (NPs) are used as delivery vehicles for pharmaceutical agents, as bioactive materials. Selenium nanoparticles (SeNPs) are gaining importance owing to their excellent antibacterial properties. Ulva lactuca (Linnaeus), a green seaweed, is reported to have potential anti-microbial properties. In this study the green seaweed Ulva lactuca (Linnaeus) is used for the green synthesis of selenium nanoparticles and its antibacterial activity against oral pathogens studied. The synthesized nanoparticles were confirmed using UV-vis spectroscopy for the surface plasmon resonance, and morphology of the nanoparticles was analysed using a Transmission Electron Microscope (TEM). The crystalline nature of the green seaweed mediated nanoparticles was analysed using X-ray Diffraction assay (XRD). The UV-vis and XRD confirmed the synthesis of SeNPs, and TEM revealed smooth spherical nanoparticles. The antibacterial potential of synthesized SeNPs was compared with commercial antibiotics by the well diffusion method. The SeNPs at 100µl concentration significantly inhibited bacterial growth against Steptococcus mutans, Enterococcus faecalis, Staphylococcus aureus, Pseudomonas sp, and Candida albicans. This study revealed that Ulva mediated selenium nanoparticles has great potential as an oral antimicrobial agent and may be used in mouth wash and related dental products development. Schlagwörter: green synthesis, oral pathogens, dental, marine algae, characterisation