Objective Hynobius leechii belongs to Amphibia, Urodela, Salamander genus, is the lower group in vertebrates.The research on its diencephalon and its position in the evolution has not been reported.By using the conventional paraffin section, HE staining, Nissl staining and silver staining of nerve fibers, we made partitions of diencephalon and localization of nuclei, discussing the histological features of genesis and development of diencephalon in Hynobius and its position in the evolution to fill the blank of study on genesis and development of diencephalon in tailed amphibians.Results The diencephalon of Hynobius was differentiated from the back-end of forebrain vesicle, the diencephalon developed slightly later than the telencephalon.The rudiment of diencephalon was formed from post-embryonic limb bud, the primordium of neural pituitary and pineal gland appeared in the incubation period.The development of diencephalon experienced the hind limb bud stage, metamorphosis stage, sub-adult stage and the adult stage, completed the differentiation and localization of nuclei in diencephalon.Taking the triangle area appeared in the back end of the middle brain as a boundary on the dorsal surface of diencephalon, the diencephalon extended itself to the rear of retuse rostral area of the mesencephalon; taking the preoptic area at the end plate in the back end of the middle telencephalon as a boundary on the ventral surface of diencephalon, the diencephalon extended itself to the end of the medulla oblongata below the pituitary.Hynobiuss diencephalon consists of the epithalamus, thalamus and hypothalamus.The epithalamus includes two parts of the pineal gland and habenular nucleus, the habenular nucleus divided into the dorsal habenular nucleus (Hd) and the ventral habenular nucleus (Hv); the thalamus consists of three parts-the dorsal and ventral thalamus and the posterior tubercle, the dorsal thalamus includes the anterior nucleus (A), the central nucleus (C) and the posterior nucleus (P); the ventral thalamus includes the ventromedial nucleus (VM), the dorsal part of ventrolateral nucleus(VLd) and the ventral part of the ventrolateral nucleus (VLv); the hypothalamus consists of the preoptic area, funnel areas and pituitary, the preoptic area includes the preoptic nucleus (POa), supraoptic nucleus (SC), magnocellular preoptic nucleus (Mg) and entopeduncular nucleus (EN).Conclusion The distribution of nuclei in Hynobius diencephalon is more concentrated, the boundaries between nuclei are less obvious than those of tailless amphibians and fish, but the asymmetry of the habenular nucleus in the epithalamus is conservative in different species.