The stomach is a dilated segment of the digestive tract which is important in many functions as continuation of carbohydrates digestion initiated in the mouth and secretion of gastric juice which is a mixture of mucus, HCL, intrinsic factor and gastric enzymes as pepsin, lipase and renin. Stomach acts as a mixed exocrine- endocrine organ that digests food and secretes hormones. It could be affected by different factors such as food, drugs, diseases and others resulting in functional disturbance and various pathological findings. For instance, cytoplasmic vacuolations, congestions of blood vessels, erosions, desquamations leading to ulcerations together with nuclear changes as shrunken pyknotic nucleus, fragmented nucleus and mitotic figures. Here, we will show the normal histological architecture of the stomach and what happens in case of gastric ulcer under light and electron microscope.