Flavonoids are natural antioxidants with a polyphenolic structure that exhibit therapeutic potential due to their anti-inflammatory, anti-cancer, antimicrobial and antioxidant properties. However, limited bioavailability and absorption in the body, poor solubility in water and instability in physiological conditions reduce their effectiveness as biologically active substances. An effective strategy to overcome these limitations is encapsulation into nanocarriers. An exceptional candidate for flavonoid delivery are mesoporous magnetite nanoparticles due to their biodegradability, physicochemical properties and superparamagnetic nature. Functionalization of nanoparticles with poly(ethylene glycol) further improves the effectivness of flavonoids by reducing the body's immune response. In the framework of this doctoral thesis, magnetite nanoparticles functionalized with poly(ethylene glycol) were synthesized by the solvothermal method. Structural, morphological, thermal and magnetic characterization of nanoparticles was carried out using different experimental techniques, and the stability of nanoparticles was tested in phosphate buffer. The mesoporous structure of magnetite nanoparticles was confirmed by Brunauer-Emmett-Teller analysis. Encapsulation of flavonoids: quercetin, myricetin and myricitrin was carried out by the adsorption method, and the efficiency of encapsulation was determined by UV-Vis spectroscopy. Structural, thermal and morphological characterization confirmed the encapsulation of flavonoids into magnetite nanoparticles. In vitro kinetics of flavonoid release from magnetic nanocarriers was controlled by combination of external permanent and oscillating magnetic fields and quantified by UV-Vis spectroscopy. The results of this doctoral dissertation indicate that a nanosystem has been developed for the efficient encapsulation of flavonoids in order to overcome their low solubility and instability in physiological conditions. At the same time, optimal conditions were found for the controlled release of flavonoids from magnetite nanocarriers using an external oscillating and permanent magnetic field.