The anatomy and ultrastructure of the digestive diverticulum of Tegillarca granosa were described using light and electron microscopy. The digestive diverticulum was situated on the gonad and connected to stomach by a primary duct. Digestive diverticulum is composed of numerous digestive tubules. The epithelial layer of digestive tubule, which is simple, is composed of basophilic cells and digestive cells. Basophilic cells are columnar in shape, and the electron density is higher than that of the digestive cell. The cytoplasm has a well-developed endoplasmic reticulum, tubular mitochondria, Golgi complex and of membrane-bounded granules of high electron density. Digestive cells were classified into three types. According to cell shape, electron density and cell organelles. However, three types of epithelia was same that striated border was observed in free surface and lysosome was observed in cytoplasm. The results of this study suggest that basophilic cells and digestive cells in the digestive tubule are specialized in the extracellular and intracellular digestions, respectively.