The normal cerebral ventricular surfaces of the hamster at all ages were studied using a scanning electron microscope with special emphasis on the development of cilia in relation to the location of ventricle and developmental stages. 1) Considerable variations of cilia were observed between individual cases even in the same developmental stages and the same ventricle. However, in general, the distribution of ciliated cells was dense on fourth and less on lateral ventricles, and the development of cilia was most advanced in fourth ventricle. 2) I the early postnatal stage, single cilium or multiple cilia of 1μ in length were seen on the surface of ependymal cells, and several rudimentary cilia were observed in places. 3) In the later embryonic stage, cilia of 1μ in length were found on the domed tip of ependymal cells of the fourth ventricle, and numerous bleb-like protrusions were observed on the surface of ventricles. 4) Fully developed cilia of 10μ in length and microvilli were recognized about 3 to 4 weeks after birth. The cilia and microvilli decreased in number as the animal age increased. 5) It is suggested that the differentiation of the surface organelles of ependymal cells may be controlled by physiological function and the dynamics of cerebrospinal fluid.