The conformational, electrooptical, and dynamic properties of polystyrene (PS) macromolecules modified with the third-generation Frechet dendrons in toluene were studied by the methods of viscometry, isothermal diffusion, and electric birefringence. It was established that the hydrodynamic dimensions of the modified PS molecules are about one and a half times larger than those of the initial PS molecules of the same generation. It is shown that the increase in dimensions of the polymer molecular coils is due to increasing equilibrium rigidity of the modified PS macromolecules. It was found that, in contrast to common PS where electrical birefringence is due to a small-scale orientation of molecules, the electrooptical effect in the solutions of dendron modified-PS is due to orientation of the macromolecules on a scale comparable to their end-to-end size. It was established that PS macromolecules modified with the third-generation Frechet dendrons have higher equilibrium and critical rigidities as compared to those of the initial PS molecules.