The purpose of this study was to describe the luminal development of the murine eustachian tube and middle ear. Thirty specimens(BALB/c), aging from gestational day 11 to postnatal day 21, were investigated using light microscopic observations. The present study also used a digitizer computer and serially sectioned temporal bone specimens for three-dimensional reconstruction to measure the volume of the eustachian tube and middle ear cavity at different gestational and postnatal ages. The first pharyngeal pouch elongated during gestational day 12 to form the tubotympanic recess. Between gestational day 13 and 14 this tubotympanic recess extended to the middle ear area. A rapid increment in the volume of the tubotympanic recess was noted between gestational day 15 and 16. At this age, a definite division of the tubotympanic recess into the eustachian tube and middle ear cavity was observed. During the postnatal period, maximum change of the middle ear volume was noted on postnatal day 11 when the mesenchymal tissue in the middle ear cavity disappeared completely.