The epithelium of the Malpighian tubules in the silk worm, Bombyx mori Linne was observed with electron microscope. The epithelium is composed of cells encircling e lumen, and these epithelial cells are divided into four distinct cellular types. Type I cells are characterized by the microvilli which are loosely packed and contain mitochondria. Also, ribosomes, mitochondria, and cell organelles are well developed in the cytoplasm and large vacuoles are seen in the basal portkon of the cytoplasm. Type II cells show that basal plasma membranes are extremely infolded and mitochondria are well developed in the cytoplasm. Type III cells have microvilli which are very slender, compactly arranged and also contain mitochondria and basal plasma membrane close to the basement membrane are infolded to be dilated canaliculi. Large mitochondria and many electron dense granules are also seen in the cytoplasm. Type IV cells have basal infoldings tending to be straight and perpendicular to the basal surface. Microvilli are compactly arranged and contain mitochondria, and many vacuoles are seen in the cytoplasm.