Magnetic orientation of isotactic polystyrene during the isothermal crystallization at 210 degrees C in the magnetic field of 6 T is studied by using the magnetic birefringence, X-ray diffraction, and infrared measurements. The orientation starts in the vicinity of the end of the induction period, that is, before the crystal growth is observed by the wide angle X-ray diffraction This suggests that some anisotropic structures formed in the induction period are responsible for the magnetic orientation. Crystals formed are aligned with the c-axis, perpendicular to the magnetic field. Crystallization process is accelerted under the magnetic field.