The results of researches of a magnetic field effect on rheological properties of both paramagnetic, and diamagnetic polymer systems are described. Influence of intensity and the direction of power lines of the magnetic field on the viscosity of magnetic liquids and magnetorheological suspensions is analyzed. Results of theoretical researches of the magnetic field effect on the diamagnetic macromolecule orientation in solutions are discussed. The data on the influence of the magnetic field on rheological parameters of cellulose ether solutions are generalized and analyzed. The rheological parameters are compared with a change of studied system structure under magnetic field. The concentration dependences of viscosity and the sizes of supramolecular particles in solutions are compared. The rheological behavior of systems in a region of phase transitions is considered. Concentration dependences of the viscosity are described by curves with a maximum which concentration corresponds to a phase transition concentration.