The results of research studies of a magnetic field effect on structure and phase transitions of liquid crystalline polymer systems are described. Influence of intensity of the magnetic field, molecular weight, and concentration of polymers in solutions on the phase diagrams is analyzed. The dependences of boundary curves on the chemical structure of polymers and solvents are discussed. Results of theoretical researches of the magnetic field effect on the diamagnetic macromolecule orientation in solutions are described. The shift of boundary curves of liquid crystalline cellulose derivative systems is compared with the energy of magnetic field stored by solutions.