Inflammation has been reported to increase zonulin levels, a protein that regulates intestinal permeability. The aim of this study was to investigate the association of serum zonulin levels with preterm labor in pregnant women. A total of 180 pregnant women between 32-42 weeks of gestation were included in the study. Among those whose gestational week is less than 37, preterm labor (group 1), normal course pregnant (group 2), and gestational weeks between 37-42 pregnant women with normal course (group 3), term labor (group 4) groups were formed. Zonulin levels were not statistically different between groups. Among the inflammation markers, only C-reactive protein levels were significantly higher in group 1 compared to groups 2 and 3. There were a total of 18/90 (20%) pregnant women with premature rupture of membranes (PROM) in the delivery groups. The mean zonulin level was higher in those with PROM (155.3±50.2 ng/ml) than those without PROM (128.8±59 ng/ml). However, there was no statistically significant difference between them. In conclusion, serum zonulin levels were not useful as a marker for predicting preterm labor. However, examining large-scale studies about the relationship between PROM and zonulin is still needed.