The oval window (or vestibular window) is a membrane-covered opening which leads from the middle ear to the vestibule of the inner ear.

Vibrations arriving at the eardrum are transmitted via the interacting ossicles from the middle ear through the membrane of the fenestra ovalis to the inner ear.

It is a reniform (kidney-shaped) opening leading from the tympanic cavity into the vestibule of the internal ear; its long diameter is horizontal, and its convex border is upward. In the recent state it is occupied by the base of the stapes, the circumference of which is fixed by the annular ligament to the margin of the foramen.