The heat setting of sewing thread is known to have some puckering. In this experiment, the P/C fabrec and polyester thread were heat setted at temperatures ranging from 70℃ to 150℃ at the interval of every 20℃ for the period of 1, 5, 10, 20 and 40 minutes resoectivly. The results obtained are as follows: 1) In general, the pre-laundering sewing shrinkage related negatively to time but realted positively to temperature. And it showed the lowest rate at 110℃. 2) In case of slack treatment, the post-laundering sewing sewing shrinkage marked the lowest rate at 130℃ while that of stretch treatment showed the lowest rate at 90℃. 3) The rates of post-laundering sewing shrinkage were higher than those of pre-laundering shrinkage, the difference between them reached the bottom when applied the slack treatment at 130℃ and the streched treatment at 110℃.