The accuracy of the structures of biological macromolecules determined by X-ray crystallography is of fundamental importance, both for the understanding of life processes and for medical applications. The resolution of the structure is thus critical, and is largely determined by the quality of single crystals. Here we report the results of applying a magnetic field and a magnetization force during growth of the snake muscle fructose-1,6-bisphosphatase and human estrogenic 17 beta-hydroxysteroid dehydrogenase crystals. For both enzyme proteins, the quality of the crystals improved with repeated assay, and their data sets were collected at significantly higher resolutions. These results coincide with a mechanism involving the reduction of convection, due to both the hydrodynamics within a magnet and the partially reduced gravity induced by a magnetization force. The density difference between the crystal and solution becomes less significant, and the sedimentation speed of the crystals is also reduced in the presence of the magnetization force.