Compared with inorganic selenium compounds (sodium selenite) and organic selenium products (selenoprotein), the observation indexes include: animal weight, hematology, biochemical indexes, organs, histopathology and so on. Results: The experimental observation indexes showed that the safety of Selenium King Capsule (nano-selenium) was the highest. Medical experiments have fully proved that the safe dose of Selenium King Capsule (nano-selenium) is higher than that of inorganic selenium and organic selenium, which is undoubtedly the most important for people taking it, even more important than its effectiveness. Nano-selenium (Selenium King Capsule) has obvious effects on anti-tumor, anti-oxidation, enhancing immunity and disease resistance, and has also been fully affirmed by medical experts at home and abroad.