The structure of yolk spheres of hen yolk was observed in state of suspension of raw and fixed materials under the light and the scanning electron microscope. The yolk spheres were composed of yellow and white yolk spheres. Their structural features were discussed on the basis of figures obtained by both types of microscopy. The surface of yolk spheres seemed to be enclosed in a wall made of certain homogeneous structures. In stored eggs, the appearance of yolk spheres changed distinctly. These morphological changes were considered to have been induced by osmotic changes of the yolk.