Considering the quantum dynamics of 2DEG exposed to both a stationary magnetic field and an intense high-frequency electromagnetic wave, we found that the wave decreases the scattering-induced broadening of Landau levels. Therefore, various magnetoelectronic properties of two-dimensional nanostructures (density of electronic states at Landau levels, magnetotransport, etc) are sensitive to the irradiation by light. Thus, the elaborated theory paves a way to optical controlling magnetic properties of 2DEG.