In this work, the curling behavior of single jersey weft-knitted fabrics produced from different structures and yarn twist directions is studied. Curling behavior was characterized in terms of curling surface in both course and wale directions. It is concluded that the curling surface value of weft-knitted fabric samples produced from the Z-twist ring-spun yarn is higher than that of the samples produced from the S-twist cotton ring-spun yarn. The comparison between different fabric structures reveals that the presence of tuck stitches in fabric structure results in a (or leads to a) lower curling surface. During the tuck loop formation, the higher yarn tension on the held loop causes them to rob yarn from adjacent knitted loops. This in turn exposes more moment though the loop and the higher curling would be expected. But the results show that the friction between the yarns in contact points has a significant effect on curling reduction. It has been figured out that the structures comprised of tuck and knit loops present lower curling phenomenon. In this study, double cross tuck and triple cross miss structures show the lower and higher curling surface values. Totally it could be stated that the structures possess miss loops have the lower curling surface in the wale direction while it is the opposite in the course direction. For structures including tuck loops, the results are quite in contrary.