Background: Preterm birth is the leading cause of newborn deaths and also the leading cause of death in children under 5 years of age. There is wide spread suspicion that subclinical infection is a common accompaniment and cause of preterm labour. Ferritin is an acute phase reactant and it increases during inflammation. Aim: The objective of this study is to measure serum ferritin level in cases of established preterm labour (PTL) as a possible marker of infection. Study Setting: This study conducted at Ain Shams University Maternity Hospital from March 2015 to November 2015. Study design:  A case-control study. Patients and Methods: The study involved 2 groups. Study population: 60 cases divided into two groups: Group (I): included 30 patients with established (PTL) between 30 to 34 weeks gestational age (GA). Group (II): (Control group) 30 patients with uncomplicated pregnancies between 30 to 34 weeks GA. Serum ferritin was analyzed in the 2 groups.  Results: The results pointed out that there was statistically significant difference between two groups as regarding serum ferritin level as p value was  <0.0001 . The median serum ferritin level in preterm labour group and control group was 150 (100 – 150) ng/ml and 20 (15 – 25) ng/ml respectively. The best cut off value of serum ferritin as predictor of preterm labour was >55 ng/ml  with a sensitivity of 96.7% and specificity of 96.7 %. Conclusion: Serum ferittin can be used as a marker of preterm labour.