The tracheal mobilization technique has enabled to increase the resectable length of the trachea. This paper reported on the results of measurement of the extensibility of the canine trachea and the effect of the mobilization technique on the tension at the site of tracheal anastomosis. The maximum extensibility of the canine trachea was found to be only 36% of the original length. Conventional techniques of tracheal elongation (Som and Narodick) were not effective enough to reduce the tension developing at the anastomotic site. On the other hand, the tracheal mobilization technique has proved to be effective for increasing the extent of tracheal resection. The clinical value of the tracheal mobilization technique was discussed based on the author's experience on 94 cases of tracheobronchial plasty.