The changes of the liver in diabetes mellitus have been paid much attention because of the role of this organ in carbohydrate metabolism. The histological changes of the liver in this disease have been reported by Chipps (1), Bogoch (2), Zimmerman (3) and others, and it has been noted that intranuclear glycogen accumulation and fat metamorphosis are the characteristic findings under light microscope. The increasing use of liver biopsy technique has made it possible to study such changes more easily in a number of diabetics under electron microscope. This report is devoted to the electron microscopic observation of the intranuclear glycogen of the liver cell in diabetes mellitus and a discussion concerning the mechanism of glycogen accumulation in the nucleus.