In normal auditory systems, the difference between the bone conduction thresholds obtained with the test ear opened and occluded in low frequency signals below, 1,000 Hz is about 10-25dB. But no difference in these thresholds suggests the presence of a lesion in the conductive mechanism. Sullivan added the differences in these thresholds at 250 Hz, 500 Hz and 1,000 Hz and called ""Occlusion Index"". In order to study the audiological significance, we have measured the occlusion index in 40 ears of normal persons, 20 ears of chronic otitis media patients and 20 ears of sensorineural hearing impairment patients. We also measured the static compliance in 40 normal ears and observed the correlation with the occlusion index. The results are as follows ; 1) Occlusion Index was 33.10±10.63 dB in normal group, 3.10±3.03 dB in chronic otitis media group, 28.10±15.17 dB in sensorineural group. 2) Static compliance in normal group was 0.61±0.31 cc(0.22~1.75 cc). 3) Occlusion Index showed inverse proportion to static compliance.