Abstract: Abstract: Selenium is an essential trace elements．Selenium deficiency and excess will have adverse effects on human health. Acid digestion and atomic fluorescence spectrum are used to determinate the content of selenium of betelnut produced in Wanning City, Hainan Province. Results show that betelnut with the highest content of selenium (average value 0.042mg/kg) are produced in Damao Area, followed by Wancheng Town (0.030mg/kg), while Beida Town and Nanqiao Town with the lowest content of selenium (average value 0.016mg/kg). Betelnut with the highest content of selenium are mainly distributed in eastern and northeastern parts of Wanning City, while betelnut with lowest content of selenium are in western part of Wanning.