A malignant glycogen-rich adenocarcinoma of palatal salivary glands is reported. Histopathology revealed nonencapsulated nests and cords of polyhedral cells showing voluminous clear cytoplasms and cellular pleomorphisms, separated by fine vascular septae. Small and large ducts were infrequently seen showing apparent transition of large ducts into clear cells. The tumor cells were PAS- and Best-carmine positive, diastase soluble, and mucicarmine and Alcian-blue negative. Ultrastructurally, the tumor cells were arranged in solid nests and cords of electron-lucent cells surrounding single or multiple lumina, and surrounded by basement lamina. Occasional fusiform electron-dense cell processes were present beneath the basement lamina. The electron-lucent cells were joined by junctional complexes, contained intracytoplasmic canals, and were filled with massive accumulations of beta glycogen particles. The electron-dense processes contained interlacing whorls of fine filaments and exhibited peripheral focal densities. The findings suggest that this glycogen-rich malignant tumor is of epithelial origin most probably of ductal cells.