The morphology and structure within the cochlear aqueduct have been investigated on the basis of a histological analysis of 234 temporal bones ranging from 12-week old to adult. Barrier membrane was found in 28.6% of the temporal bones examined, and fibrous reticular tissues of the inner opening of the cochlear aqueduct in 38.1% of the temporal bones. No any tissue in the inner opening of the cochlear aqueduct was seen in 33.3%. Periotic duct was filled with loose reticular tissue. The clinical significance of contents in the cochlear aqueduct was discussed.