For the purpose to determine what effects operative hearing restoration would hays on the speech and language development, this study was carried out on 13 cases of deaf children aged 8-16 years with bilateral congenital middle ear malformation whose hearing acuity was restored within 30 db loss in average of speech range by standard fenestration operation or stapes surgery and maintained one year after the operation. Examination was carried out on the hearing ability, intelligence, lipreading, intelligibility of articulation for monosyllables, words and sentences, conversation intelligibility, sonagram of monosyllables, time of reading, total disfluency index, vocabulary and sentence structures, and these results after the operation were compared with those before the operation. The results of the study briefly presented in the following. 1) The articulation score for monosyllables, words and sentences by pronounciation was moderately improved except in two children of delayed mental development. The obtained articulation score was in the ascending order of monosyllables, words and sentences. 2) In two children with delayed mental development the articulation score improvement was only slight as compared with the other children. 3) With exception of two cases the operation for hearing restoration was found to have increased the articulation score for syllables more than fifty percent. 4) The intelligence quotient, conversation intelligibility and total disfluency index were not improved so much as expected. 5) The number of childrens' vocabulary increased markedly after the operation. 6) For the development of speech and language in deaf children with bilateral malformation of conductive apparatus, it is desirable to diagnose as early as possible in order to enable earlier operation for hearing improvement.