The fine structure of the silkglands in the fifth larval instar and prepupal stages of Pieris rapae L. was studied with the aid of light and electron microscopes. 1. In the early stage of the fifth larval instar, the free ribosomes remakably appeared, while in the middle stage the rough endoplasmic reticulum and Golgi vacuoles increased in the cytoplasm. 2. In the later stage of the fifth instar, the rough endoplasmic reticulum slightly reduced, and the secretory globules derived from the Golgi vacuoles increased in number, accumulated around free surfaces, and were secreted by the exocytosis into the lumen. 3. The Golgi vacuoles were rapidly reduced in the early prepupal stage, whereas the mitochondria decreased and the autophagic vacuoles formed by the autophagosome appeared in the middle prepupal stage, and then were transformed into vacuoles. 4. In the later prepupal stage, the nucleus was crushed in shape, and the vacuoles fused with each other and were gradually vacuolizated from the free surfaces.