Recently, a superconducting magnet has been used to obtain better quality crystals. The time dependence of the birefringence (Deltan) of protein solutions caused by the application of a strong magnetic field was studied. For the solution from which crystals are easily formed, An increased with time when a uniform magnetic field of 10 T was applied, Deltan showed the tendency to increase with increase in the concentrations of lysozyme and NaCl. Deltan continued to increase even after shutting down the field. If the protein solution was never exposed to the field, Deltan did not increase. The appearance of Deltan suggests the molecular ordering along the direction of a magnetic field in the solutions from which crystals are easily formed. These results can be explained by considering the formation of an interlinked network of protein molecules under a high magnetic field.