A study on the acoustic reflex threshold and reflex decay was performed in 240 ears that had normal hearing and type A tympanogram without history of ear diseases. The results are as follows : 1) Average value of acoustic reflex threshold was 76.5 dB SL and decreased with aging, but there was no significant difference between both sexes. 2) The acoustic reflex threshold was highest at 2,000 Hz in all age groups and lowest at 500 Hz in the age group under 20 years and at 1,000 Hz in the age group over 21 years. 3) There was no significant difference between ipsilateral and contralateral reflex threshold. 4) The acoustic reflex decay was noted at frequencies over 2,000 Hz and it was most frequent in the first decade, but there was no significant difference between both sexes. 5) The absence of acoustic reflex was noted at frequencies over 4,000 Hz.