Nanobiotechnology is an actively developing field of science, which finds application in cancer therapy, molecular diagnostics and molecular imaging. In this work, selenium nanoparticles were successfully obtained by chemical reduction of selenite ions with ascorbic acid in dextran phosphate (DP) solutions, which was used as a stabilizer. It has been found that dextran phosphate coated nanoparticles are stable during storage for 3 days. Sorption of the antitumor substance doxorubicin was studied in the concentration range from 0.1 mg/ml to 1 mg/ml. A significant prolongation of cytostatic release from stabilized nanoparticles was shown. Selenium nanoparticles coated with water-soluble DP can be used to create broad-spectrum drugs, in particular, antitumor drugs that compensate for selenium deficiency in the body.