The changes of the structure in oocytes during the oogenesis of Litopenaeus vannamei were studied with transmission electron microscope. The results showed that the structure was simpler and the active metabolism is lower in oogonium. The particles from the nucleus mainly passed through the perinuclear cisternae into the cytoplasm because of fewer nuclearpores. The marked changes occurred in the latter previtellogenic oocytes and the primary vitellogenic oocytes. The nuclear changes consisted of the concavo-convex nuclear membrane, many more nucleoli, numerous nuclearpores and a large amount of nucleolns granular materials penetrating nuclear membrane into cytoplasm. There were various well-developed organelles in the cytoplasm which exhibited higher synthetic activity. The yolk granules formed mainly in active vitellogenesis. At this stage, a lap spherical cortical rods appeared radializedly at the edge of the cytoplasm. Meanwhile active microphagocytosis could be seen along the ooplasma membrane while the vitellin membrane formed on the surface of vitellogenic oocytes. The mature oocytes were fill of big yolk granules and lipid droplets and the number of organelles reduced quickly. The relation between the changes of the structure in oocytes and the vitellogenesis was discussed. The origin and function of the cortical rods were also discussed.