Cross-section transmission electron microscopy (TEM) specimens were fabricated by a focused ion beam etching for the purpose of investigating the layer structure of multilayer coated x-ray mirror. Uniform samples 0.1 mum wide, 4 mum tall, and 10 mum long were prepared. The structure of a Ni-C multilayer film was observed over a large area. Good agreement between the multilayer periods obtained by TEM and diffraction analysis was found.