Abstract: This work focused on histological study on head kidney and spleen in Eleutheronema tetradactylum. The results showed that head kidney, the soft parenchymal organ with brown color and rough surface was located in the backside and around the spinal cord. Under optical microscopy, no renal tubular was found in head kidney encysted by collagen fiber, which filled with numbers of lymphocyte, hematocyte, granulocyte and macrophage, but melano - macrophages center（MC）was not obvious. Spleen shaped as “triangle”, larger in volume and color in brown, staying in junction between intestine and the end of stomach. The spleen was made up of red pulp and white pulp with capsule covering outside, and spleen trabecular structure consisting of expanding connective tissue was obvious. In red pulp, large number of blood cell crowed together being the splenic cord， between this item was splenic sinus, there often had multiple MC; large number of lymphocytes distributed in white pulp with blood vessels going through the center. The features of spleen and head kidney in E.tetradactylum indicated that they are typical immune and hematopoietic organs.

Key words: Eleutheronema tetradactylum, head kidney, spleen, histology