Since clinical study of impedance measurement in 1946, many studies have been made. The impedance measurement is valuable especially in the application of impedance measurement in the assessment of ear disorders in children and the objective assessment of middle ear disorders. But we have not made a complete explanation in the motility of eardrum, the air cushion of middle ear cavity and the status of ossicular chain yet. Now the authors studied experimentally with dog's ears how the mass of eardrum itself affects on the impedance change. The results are as follows ; 1) The tympanogram and the static compliance in dogs' ears are almost similar to those of men. 2) The type of tympanogram is not transformed by the increase of eardrum thickness itself. 3) The maximum compliance is increased by 0.54cc per one cellophane patch(2.2cc per the doubling of eardrum thickness) and the static compliance is decreased by 0.07cc per one cellophane patch(0.28cc per the doubling of eardrum thickness). 4) We conclude that the above results are considerably valuable in the clinical diagnosis of the eardrum disorder itself.