Ultrastructure of the mature ovary of the wax moth, Galleria mellonella, consisted of eight polytrophic ovarioles in a pair of ovaries was studied with electron microscope. At the germarial region of the ovariole the stem line oogonia differentiates to a oocyte and nurse cells, and the follicular epithelial cells surround the oocyte, forming a separate follicle. At the vitellial region yolk synthesis is very active within the oocyte. As a consequence of that the oocyte contain compactly aggregated glycogen particles and yolk granules. The ovarial sheath of the ovariole comprise two kinds of layers-tunica propria and connectives. The tunica propria is an elastic membrane containing fine fibrils, and the connectives have two directional bundles of the muscle fibers oriented circular and longitudinal directions. During the vitellogenesis, the nurse cells degenerated gradually, and pinocytotic vesicles formed along the oocyte plasma membrane makes proteid yolk granules by the vesicular fusion. At this period two kinds of follicular epithelial cells appeared. More common form surrounds the peripheral ooplasm, and has a cuboidal or slightly columnar shape. But the less common form has a flat or squamous shape occurs only between the oocyte and nurse cells, and has enlarged cisternae of the rough endoplasmic reticulum. After yolk synthesis two kinds of egg membranes, vitelline and chorionic membranes, are formed. In the cytoplasm of the mature egg electron dense proteid yolk granules and electron lucent lipid yolk granules are compactly aggregated, and surrounding follicular epithelial cells being degenerated completely.