This study was designed to investigate the volume of mastoid antrum and pneumatic cells as a factor in determining the compliance at the ear drum. 56 cases (105 ears) ranging in age from 14 to 45 year old who have no definite middle ear pathology were tested with static compliance and radiologic examination of temporal bone by Law's and Townes' views, and two tests results were compared with each other. Results of static compliance by the degree of peumatization indicated that the medians of static compliance were 0.98 in W, 0.57 in W, 0.63 in W+, 0.5 in U+, 0.47 in U, and 0.23 in U. The findings of cases with no middle ear pathology in static compliance and degree of pneumatization of temporal bone suggested that the static compliance is in direct proportion to the degree of pneumatization of temporal bone and therefore this is an important factor in determining that.