The resectable length of the trachea depends closely upon its mechanical properties, especially the elasticity. Accordingly, it is essentially important, in cricohyoidopexia or end to end anastomosis of the trachea, to obtain preoperative information concerning with the extensibility of the trachea. Such a preliminary imformation might contribute to good postoperative results.In the present paper, a new method assessing elastic properties of the trachea will be described. This method has been called Yerzley's Resilience, originally representing the dynamic elastic modulus of the viscoelastic materials. expresses the ratio of recovery energy against given energy in percentage. In this study, a single rectangular mechanical impulse was given to the trachea under various longitudinal tension, and vibratory patterns of the trachea were recorded by the ultrasonic pulse variant M-mode display. Then, resilience values were estimated from a freely decrementing curve thus obtained, using the given formula.Twelve resected fresh canine tracheas were investigated under the condition of simple longitudinal elongation. In addition, 10 canine tracheas fixed with 10% formaldehyde solution were investgated in the same manner. The results obtained are as follows;1) values of the tracheas measured immediately after resectionUnloaded mean value was 67.9%, and as tension increased, as rose the value rapidly until the level of 300g loading. Then, the rising pattern of the value leveled off, and finally when loading reached 1, 000g, resilience value was 87.9%.2) values of the tracheas fixed with 10% formaldehyde solution for 1 week Unloaded mean value was 82.3%, 1.21 times higher when compared with the value described above. The increase in resilience value was not remarkable even when the tension increased.3) Relationship between resilience values and stress-strain curveA stress-resilience curve obtained by measuring resilience values nuder various longitudinal tension upon trachea well corresponded to a stress-strain curve.In conclusion, the results obtained suggest that the evaluation of Yerzley's Resilience of canine trachea can well express its mechanical properties warranting further investigation of the mechanical properties of the human trachea in vivo using a similar method.