It has been well known that a well functioning eustachian tube is an essential prerequisite for postoperative aerated middle ear space. Testing the patency of the tube is at present one of the routine preoperative examination and a number of tests have been presented from which quantitative information is gained on the function of the eustachian tube. There has always been much discussion about the relation between the size of mastoid air cell system and chronic otitis media. Tumarkin contend that frustration of pneumatization results from failure of aeration of the middle ear cleft, due to blockage of the eustachian tube. The intramastoid negative pressure could occur by persistent obstruction of eustachian tube and interfere with the mastoid pneumatization. The authors studied a total of 87 ears with central tympanic membrane perforation of 68 patients, who visited to S.N.U.H. ENT OPD. For evaluation of the tubal function the negative pressure equalization test was performed according to Flisberg et al by means of an electroacoustic impedance bridg(TA-3D) and mastoid view was taken. Sixteen ears showed residual pressure of 9~-19mm H₂O, 31 ears showed -20~-199mm H₂O and 40 ears remained in -200mm H₂O. Mastoid air space measured by planimetric method revealed 8.73cm² in control ears and 3.50cm² in chronic otitis media. Normal tubal function was found in 13.3% of cases with mastoid air space under 3cm2, 14.3% in air space with 3-6cm², and 42.9% in air space over 6cm². This shows close relationship between tubal function and mastoid air cell system.