Various methods have been used in the treatment of middle ear effusion. The best treatment is the myringotomy and ventilating tube introduced by Armstrong in 1952. Through the use of pure tone audiometry and impedance audiometry we clinically observed 30 cases of middle ear effusion(54 ears). The following are the results : 1) Tympanograms of the secretory otitis media patients revealed 13% with Type A, 83% with Type B, and 4% with Type C. 2) The static compliance was distributed in a range from 0.01cc to 0.70cc with the average being 0.15cc. 3) If both ears was involved, there was bilateral absence of acoustic reflex. In the cases of the unilateral ear involvement, the acoustic reflex was absent or the threshold was elevated when stimulated by sound. Also, the acoustic reflex was absent when the sound stimulate the intact ear. 4) The nature of the middle ear fluid was as follows : 50% serous exudate : 43% mucoid exudate : in the remaining 7% either there was no exudate or the nature of the exudate was non-definable. 5) Treatment by myringotomy and ventilating tube resulted in postoperative marked improvement in air conduction hearing acuity. In those ears that had developed a serous exudate, the degree of preoperative hearing loss was smaller and postoperative hearing improvement was greater. 6) There was almost no difference in hearing acuity according to tympanogram type.