Selenium nanoparticles have found applications and are used extensively in food science and biomedicine because of its higher biocompatibility and low toxicity nature. Selenium is originally an important factor in the process of selenoproteins formation as vital antioxidant-like agent. Selenium nanoparticles have strong free radicals suppressing impacts in vitro and in vivo and can protect nucleic acids and DNA against oxidative damage. In addition to this, selenium nanoparticles have been shown to have anti-carcinogenic behavior against some cancers and reported cases of antimicrobial properties. Moreover, they are used as nutritional supplements, diagnostics, nanotherapeutics and even as medical devices. Selenium nanoparticles have industrial applications as photocopiers xerography rectifiers and in solar cells. Selenium nanoparticles can be synthesized following chemical, physical and biological methods. The chemical and physical methods involve the synthesis at higher temperatures and at acidic pHs. The biological methods, however, have no hazards and toxicity of the chemical methods. Due to natural coatings by agents, the particles synthesized according to the biological procedure are more stable and have no agglomeration.