This paper presents the effects of elastane yarn type and fabric density on the seam performance of PET/ elastane woven fabrics. In this study, 12 different weft stretched fabrics were woven with 2 different weft yarns, 2 different weave types and 3 different weft densities. The weft and warp yarns of the weft stretched fabrics were polyester-elastane covered yarn and polyester yarn, respectively. Air-covered and twisted elastane weft yarns were used at twill and plain fabrics. Needle penetration forces were determined on an L&M Sewability tester for seam performance. Besides this, "needle damage index" was calculated for seam damage. The values of the needle penetration forces were between 64 cN and 370 cN and the needle damage index values were between 18% and 73%. Elastane yarn type and fabric density had significant effects on the needle penetration force. Photographs were taken with an optical microscope to show the seam damage during sewing.