Fin structure of the dorsal vessel in Galleria mellonella L. was studied using scanning and transmission electron microscopes. The dorsal vessel was composed of 9 abdominal segments as the heart, and 3 thoracic segments as the aort. Heart containing ostial valves, but aorta was a simple tube. The dorsal vessel wall consisted of the inner and outer membrane of the myocardium which was located between them, and covered with fibreous membrane. Myocardium was striated and a slow muscle, and each thick filament of the myofilament was surrounded by 6 thin filaments. The peripheral cell bounded the heart wall contained many vacuoles. The cluster of the pericardial cells connected with heart, and its cell contained Golgi complex, coated vesicle and secretory granule, and peripheral cell seems to carried out endocytosis and exocytosis. Each alary muscle of the segment divided into several branches at the points of their attachment to the peripheral body cuticle. These branches were interconnected with connective tissues forming a mesh shape.