In order to obtain information of the functions of the hearing aids and the trends of the hearing aid settings in the aids of the hearing impaired children in Seoul, randomly sampled 41 hearing aids of the preschoolers and 31 hearing aids of the 4th and 5th graders in the primary schools were investigated on the gain, tone control, SSPL-90, harmonic distortion and mechanical problems as they are worn : 1) Mechanical problems were observed in 14.6% of the aids from the preschools and in 38.7% of those from the primary schools. 2) The mean and standard deviation of the harmonic distortion of the total hearing aids were 4.5% and 9.4%, respectively. Harmonic distortion decreased as frequency increased and increased as intensity increased. The harmonic distortion of the aids from the primary schools were greater than those from the preschools. 3) The aids with harmonic distortion greater than 10% were 3.3% of the total aids at the input intensity of 50 and 60 dB SPL, but it increased to 16.7% and 41.7% as the intensity was increased to 80 and 90 dB SPL, respectively. 4) The average gains were lower than the gains specified by Libby in the aids both from the preschools and from the primary schools at all frequencies. Gains within plus or minus 10 dB of Libby's criteria were observed in 22.2% of 126 frequencies among the aids of the preschoolers and in 21.9% among 64 frequencies of the aids from the primary schools. Most of the rest of the frequencies exhibited gains much smaller than Libby's criteria. The average gains of the aids from the preschools were greater than those from the primary schools. The frequencies with the closest gains to the Libby's criteria was 250 Hz followed by 2000 Hz. 5) Less than one third of the wearers heard the amplified speech of normal conversational level at the frequencies between 250 and 1000 Hz and no one heard the pronunciation of 2000 and 4000 Hz. 6) Hazardously high level of SSPL-90 compared with the degree of the hearing loss were observed in 7 children(21.9%) from the preschools only.