Using a wide-field Kerr microscope, we have studied the magnetic domain structures of epitaxial and polycrystallineLa0.67Sr0.33MnO3thin films as well as a film having thermally induced ⟨110⟩ microcracks. The epitaxial film on a (001)SrTiO3substrate has different magnetic domain behaviors for in-plane fields applied along the ⟨100⟩ and ⟨110⟩ directions. Magnetic domain orientation and contrast suggest a biaxial magnetic anisotropy with ⟨110⟩ easy axes. Defects such as microcracks and grain boundaries have a strong perturbing effect on the local magnetization and can lead to an enhanced and controllable spin-dependent scattering. ©1997 American Institute of Physics.