It has been well known that the selection of maximum power output in hearing aids fitting is important. In general, it was determined through the uncomfortable loudness level (UCL) test. The purpose of this study was to measure and compare the UCL and acoustic reflex threshold (ART) in young normal children and adults for early intervention and aural rehabilitation, including hearing aids fitting for hearing-impaired children. Pure tone hearing threshold, UCL and ART were measured in 40 ears of children and adults with normal hearing respectively. In results, UCL was higher than ART by 8.9 dB in children and was similar to ART in adults. And UCL, dynamic range (DR) and ART of children was higher than that of adults by 12.0 dB and 3.6 dB. In conclusion, we would suggest to monitor environmental noises properly and thoroughly for children's hearing based on the our results.