The utilization of Ziziphus oenoplia and selenium nanoparticles in dental varnish formulations presents a novel approach to enhancing antimicrobial and antioxidant properties. This study aimed to synthesize eco-friendly selenium nanoparticles and evaluate the cytotoxic and embryological toxic effects of a dental varnish composed of these nanoparticles and Ziziphus oenoplia. The plant extract was prepared using Ziziphus oenoplia, and selenium nanoparticles were synthesized with sodium selenate and distilled water. The cytotoxic effects were assessed using the Brine Shrimp Lethality Assay. Results indicated that a concentration of 10 μg/ml did not impact the viability and hatching rate of live nauplii. However, increasing the concentration to 20-40 μg/ml negatively affected both the hatching rate and viability. This study underscores the potential of incorporating Ziziphus oenoplia into dental varnish, while also highlighting the need for further research to evaluate the toxic effects of selenium nanoparticles as a component of dental varnish.