The study reported in this work concerns the influence of sewing conditions such as the distance between seam line and fabric edge, seam direction (cutting angle relative to weft yarns), number of stitches per unit length of seam and the linear density of sewing threads on the seam breaking strength and extension of woven fabrics for both double lock and single-thread chain stitches. The application of fractional factorial design to optimize the operating conditions of sewing machine is demonstrated. The optimum sewing conditions when using double lock stitch are the distance between seam line and fabric edge is 2cm, the seam line is parallel to the selvedge using 5 stitches/cm and the linear density of sewing thread is 70/3 Ne. But when using single thread chain stitch the optimum conditions are the distance between seam line and fabric edge is 1 cm, the seam line is parallel to the selvedge using 3 stitches/cm of 50/3 Ne sewing thread count. Also the optimum sewing conditions for seam extension could be determined for both the double lock and the single – thread chain stitches. When using single – thread chain stitch, it gives the highest seam strength and the lowest seam extension compared to the common double lock stitch.