Abstract: Ultrastructural changes in the fiber of Phyllostachys edulis (Carr.) H. De Lehaie culms during the developmental process were investigated with transmission and scanning electron microscopy. The results suggested that mitochondrion, rough endoplasmic reticulum, Golgi bodies, lomasomes and cortical microtubules were correlative to the formation of primary wall and secondary wall of earlier stage. In the earlier stage of secondary wall formation, chromatin agglutination, swelling and disintegration of organelles, and multivesicular bodies, etc. appeared in fiber cytoplasm. Fiber nucleus with the chromatin agglutination would keep for a long time, which implied that secondary wall formation stage of fiber in Phyllostachys edulis culms was a programmed cell death. Along with the further development of fiber, secondary wall continued thickening: the thickening level obviously increased in the former 4 years, and then gradually decreased. During the secondary wall formation,polylaminate structures of wall appeared in the fiber, with the persistence of plasmodesmata and transfer vesicles between fiber and its surrounding cells. The persistence of nucleus and plasmodesmata indicated the characteristic of long-lived cell of fiber.