|| In spite of the importance of endocochlear DC potential (EP) and the K+-rich endolymph for the avian cochlea, the structure and function of the tegmentum vasculosum (TV) has not yet been fully elucidated, compared with those of the stria vascularis in the mammalian cochlea. In this study, we examined structural analysis of the epithelial cells, gene expressions of Na+-K+-ATPase (Atp1A1) and Kir4.1 (Kcnj10), and protein localizations of Na+-K+-ATPase and Kir4.1, in the TV. Tight junctional structures were observed between epithelial dark cells and light cells in the TV. Both Atp1a1 and Kcnj10 genes were detected in the TV. In addition, immunopositive signals for both Na+-K+-ATPase and Kir4.1 were recognized in the TV. These results indicate that Na+-K+-ATPase and Kir4.1 play roles in maintaining the EP and high K+ concentration of the endolymph. Further studies are needed to clarify the physiological functions of the TV. This is the first report which demonstrates that gene and protein expression data contribute to the avian inner ear homeostasis.