A sheet material for a seat characterized in that the stress at 5% elongation (A) is from 40 to 300 N/4 cm width wherein A is a larger value between a stress measured in the longitudinal direction and a stress measured in the lateral direction, that the ratio A/B is from 1.5 to 15.0 wherein B is the smaller value obtained in the above measurement, and that the reduction in width (H) is from 0 to 15% when the sheet material is fixed on a frame at the one end and the opposite end while stretched and pressured.