Background: Preterm birth (PTB), defined as delivery before 37 completed weeks of gestation, remains a major cause of neonatal morbidity and mortality globally, with Bangladesh reporting one of the highest prevalence rates worldwide. Zinc, an essential trace element involved in immune regulation, oxidative stress modulation and hormonal balance, has been hypothesized to influence gestational duration. This study aimed to evaluate the association between maternal serum zinc level and preterm birth. Methods: This case-control study was conducted at the Department of Obstetrics and Gynaecology, Bangladesh Medical University (BMU), (former BSMMU), Dhaka, from September 2022 to August 2023. Sixty pregnant women aged 18–40 years, at 28 to <42 weeks of gestation, presenting in spontaneous labour with intact membranes and delivering a live singleton baby, were enrolled. Thirty women who delivered before 37 completed weeks constituted the cases, while 30 women with term deliveries served as controls. Serum zinc levels were measured using a colourimetric method on a Thermo Scientific™ Indiko™ Plus Clinical Chemistry Analyzer. Results: Maternal serum zinc was significantly lower in the case group (68.13 ±32.73 mcg/dL) compared to controls (102.41 ±60.97 mcg/dL) (p=0.009). Women with zinc levels below 68 mcg/dL had 4.7 times higher odds of preterm birth than those with levels ≥68 mcg/dL (OR=4.667; 95% CI=1.571–13.866; p=0.001). Socio-demographic, obstetric and anthropometric variables did not differ significantly between groups. Conclusion: Low maternal serum zinc level was significantly associated with preterm birth. Serum zinc estimation may serve as a potential predictor for preterm birth risk and supports consideration of routine zinc supplementation during antenatal care.