Polyester filament sewing thread was treated with wax. The sewability was evaluated from the maximum speed of the sewing machine, with which the T/C woven fabric could be sewn over four meters long without thread breakage. The frictional coefficient measured by Capstan method. The frictional coefficient depended on the wax content, the frictional speed, and the temperature of frictional body. It decreased abruptly in the 0~0.3% range of the wax content, and kept the increasing according to the wax content increment. The sewability was improved very much in the 0~0.3% range, and kept the highest level at 1.3% of the wax content. It was suppressed with the excessive wax content.