The oviduct fluid mainly derived from the oviduct epithelium is reported to provide the environment necessary for embryonic development. To elucidate the origin of glucose in the oviduct fluid, we examined the expression and localization of glucose transporter 1 (GLUT1) in the rat oviduct by Northern blot analysis, immunoblot analysis and immunohistochemistry using both light and electron microscopy. Northern blot and immunoblot analyses both showed the presence of the GLUT1 mRNA and protein. Specific staining for GLUT1 was observed in the ampulla and the isthmus, but only slightly in the fimbria and the utero-tubal junction. Staining was confined to the luminal surface of the epithelial mucosa. Immunoelectron microscopic analysis revealed that GLUT1 was observed only on the surface of the microvilli in non ciliated secretory cells, but not in ciliated cells. These findings suggest that GLUT1 plays an important role in the glucose transfer from the oviduct epithelium into the lumen and in maintaining the adequate glucose concentration of the oviduct fluid for embryonic development in rat oviduct.