Selenium nanoparticles (SeNPs) have the capacity to be used for various purposes . Therefore, they have attracted more attention in recent years and several synthesis methods have been exploited. Green synthesis or biological synthesis using plant extracts or bacterial synthesis has gained popularity . AIM: To prepare and assess the toxicity of the selenium nanoparticles prepared using Cocos nucifera (tender coconut). MATERIALS AND METHODS: Water from Cocos nucifera was obtained and used in the green synthesis of selenium nanoparticles from sodium selenite and ascorbate. Brine shrimp lethality assay and Zebrafish toxicology were performed to evaluate the toxicity of the prepared material. RESULTS: Selenium nanoparticles synthesised from Cocos nucifera said to possess cytotoxic effect against the cancerous cell . Cytotoxicity of selenium nanoparticles synthesised from Cocos nucifera depends on the level of concentration through that therapeutic effect can be studied . CONCLUSION : Cytotoxicity of selenium nanoparticles synthesised from Cocos nucifera depends on the level of concentration through which therapeutic effect can be achieved