The purpose of this study was to define the histopathological changes in the temporal bone of a fetus with trisomy 18 syndrome, a stillborn due to perosplanchnia. Several anomalies were found including malformation of the auditory ossicles, residual mesenchyme in the middle ear, aberrant tensor tympani muscle, absence of stapedial tendon, aberrant lateral ampullary nerve and wide endolymphatic sinus. The incus body was deformed and separated from the long process by connective tissue and monocrural stapes was noted in the right ear. Three-dimensional reconstruction images provided a clear view of the auditory ossicle malformation. The abnormal findings in our case indicate that ear anomalies in this syndrome might be derived from the component around the first and second branchial arches.