Cochlear aplasia of inner ear is rare congenital deformity. In recent years, high resolution computed tomograms are helpful in identifying inner ear anomalies, especially in patients with sensorineural hearing loss. The authors experienced a case of cochlear aplasia with lateral semicircular canal dysplasia sufferring from unilateral hearing impairment since 9 years old. On neurotologic examination, anomalous side ear was deaf and no response to vestibular function test. But middle ear cavity and ossicles were normally developed on radiologic examination.