Air-jet textured, textured-twisted and textured-pli ed yarns have been made from apparel -grade polyester flat yarns and compared with commercial cotton a nd spun polyeste r sewing threads for prope rti es a nd seam efficiency. The uniformity characteri stics of air-jet textured sewin g threads are far superior to those of cotton and spun polyeste r threads. The tenacity , loop stren gth and knot strength of textured sewing threads are lowe r than those of spun polyester threads but sli ghtl y better th a n those of cotton threads. Textured threads have hi g h friction values than commercial threads. The seam effic ie ncy of fabrics stit c hed with textured threads is hi ghe r compared to that of fabrics stitc hed with cotton threads and close to th at of fabrics stitc hed with spun polyester threads. Minimum knot strength has a good correlation with seam effic ie ncy.