Objective: The aim of the current study was to determine serum endocan levels in patients with threatened preterm labor and to assign whether endocan levels in patients with true preterm labor who give birth within 7 days differ from those of false preterm labor and uncomplicated pregnancy. Materials and methods: This cross-sectional study was conducted on 58 patients diagnosed with threatened preterm labor and 31 healthy pregnant women matched for gestational age. Patients with threatened preterm labor were divided into two groups; preterm delivery (28) and term delivery (30) groups. Maternal serum endocan levels were measured with the use of an enzyme-linked immunosorbent assay kit. Results: The median serum endocan level (pg/mL) in patients with threatened preterm labor was significantly higher than that of women with uncomplicated pregnancies (725, IQR 619-823 versus 310, IQR 218-423; p < .001 Figure 1). Subgroup analysis performed among threatened preterm labor group revealed that median serum endocan level (pg/mL) in preterm delivery group was higher compared with the other two groups (preterm 823, IQR 718-905 versus term 637, IQR 590-729 p < .001 and preterm 823, IQR 718-905 versus control 310, IQR 218-423 p < .001). The threshold value of maternal serum endocan level for predicting delivery within 7 days after admission was calculated 655 pg/mL, (the area under curve was 0.934, 95% CI 0.88-0.98, p < .001) with 85.7% sensitivity and 78.7% specificity. The mean cervical length measurement was significantly higher in the control group (p < .001); there was no significant difference in cervical length between the term and preterm delivery groups. Maternal characteristics including age, BMI, gravidity, gestational age at blood sampling, CRP and Hb levels were not significantly different between groups (p > .05). Conclusions: The maternal serum endocan level may be a useful marker to define high risk group for preterm delivery in patients with threatened preterm labor and similar cervical length measures.