Effects of frequency of intermittent sounds on duration estimation were examined with the subject of 155 children, from three to nine years of age, together with 20 adults. The main results were as follows: (a) the duration accompanied by intermittent sounds, of which the frequency was 2.5, 5.0 or 10.0 s-1, was estimated longer as the frequency of the sound was higher, (b) the effect stated in (a) was most optimal at the age of six and the effect decreased as the age increased, and (c) below the age of six, the effect was less conspicuous and unambiguous. These findings were explained by Matsuda's model for the duration estimation.