75 ears of 44 patients with secretory otitis and 80 ears of 40 patients with normal ear were observed and reserched. All of the cases were received X-ray examination of mastoid process in Schuller's lateral projection. The size of the air cell system was obtained by planimetry: the method what was originally devised by Diamant. The outline of the mastoid air cell system (MACS) was marked out on the radiograph and then transferred to graph paper where the number of mm2 can be counted directly. According to measuring the planimetric area of MACS. The mastoids were divided into two categories: pneumatization type and nopneumatization type. 5 of 69 ears with pneumatization mastoid (7.2%) were secretory otitis, while 70 of 86 ears with nopneumatization (81.4%) were secretory otitis. It was significantly different (P < 0.001) camparing the number of ears with secretory otitis. We believe that the degree of mastoid pneumatization is associated with the occurring and prognosis of secretory otitismedia.