Selenium is an essential trace element for human body. Flavonoids have been well characterized as antioxidant, antibacterial, anticancer, and immunomodulatory agents. Therefore, a luteolin–selenium complex has been synthesized from selenium dioxide and a flavonoid luteolin. Studies of the structure of the generated complex and mechanism of its formation have indicated that the generated complex contained two luteolin units and one selenium oxide group attached to the two sixth-position carbons of luteolin units. Conversion rate for the complex is determined to be 25.3% of the mass of luteolin, and the selenium content is 11.88% of the mass of the complex.