Fifty-eight children (from 4 to 19 years of age) with bilateral, symmetrical, sensorineural hearing loss, who had used a hearing aid in only one ear for 1 to 19 years were investigated to study the influence of hearing-aid upon the residual hearing between the used and no used ears. The results were as follows, 1) The average hearing level for the used ear at seven frequencies was 49. 5 dB of pre-hearing-aid usage and was 53. 8 dB of post-hearing-aid usage. The discrepancy of audiograms between the aided and unaided ear was not remarkable. 2) The hearings for both the aided and the unaided ears in Audiograms was progressive for a long time. But no significance relation was observed between changes in used-ear hearing of the aided and unaided ears. 3) When the hearing levels of the children were scrutinised on an individual basis, it was found that 9 cases (15.5%) in both ears, 2 cases (3.4%) in only used ear and 1 case (1.7%) in only no used ear out of 58 cases showed deterioration of hearing. 4) These data did not lead us to the conclusion that hearing-aid usage was detrimental on the residual hearing of children with sensorineural hearing loss.