The objective of this work was to study the histological structure of the dog's coro‐ nary artery by light and transmission electron microscope (TEM). The coronary artery consisted of three tunics: tunica intima, tunica media and tunica adventitia. The tu‐ nica intima consisted of endothelium rested directly on internal elastic lamina with‐ out the subendothelial connective tissue layer. The tunica media were composed of smooth muscle fibres interspersed with few elastic and collagen fibres. The tunica adventitia consisted of collagen and elastic fibres intermingled with fibroblast cells; it had vasa vasorum and nervi vasorum. Some histomorphometric measurements were performed and compared statistically. The ultrastructural study showed that the en‐ dothelial cells were communicated through complex junctions and characterised by filiform cytoplasmic processes passed through the opening of the underlying internal elastic membrane. The smooth muscle fibres of tunica media communicated with each other through cytoplasmic processes. The tunica adventitia showed minute non‐myelinated nerve. This work revealed that the dog's coronary arteries are typical muscular arteries, which show little structural variations from that of other mammals