The effects of swelling of lyocell fiber and yarn on fabric structure have been studied. As the concentration of NaOH solution increases, the degree of swelling of lyocell fiber and yarn increases together up to the critical concentration, above the critical concentration, the degree of swelling starts to decrease. The swelling of lyocell yarn causes fabric thickness to increase and fabric length in warp and weft directions to decrease. This is due to the fact that yarn inflates in the direction perpendicular to the fabric surface when excessive swelling occurs. The amount of contraction in warp direction is greater than weft direction because of the differences in crimp and tension applied to the yarn during weaving. Also yarn length changes after swelling and drying because of structure change of yarn. Yarn length after drying is longer than after swelling. This is due to the relaxation of the induced stress by swelling and the reduction of restrictions between fibers. The structural change of swollen fabric by drying is not much, therefore, the status of swollen fabric is very important.