The link between maternal periodontitis and preterm birth has increasingly received attention, but the results were still inconclusive. This study aimed to examine the association between periodontitis and preterm birth. Cases were 130 women who delivered a live singleton newborn before 37 weeks'' gestation. A random sample of 260 women, who delivered normal birth at the same day as the cases, were selected as controls. Periodontal examination was performed within 24 hours postpartum at bedside. Others related information were collected by a structured questionnaire and medical records. Multiple logistic regression analysis was performed controlling for socioeconomic,nutritional status, obstetrical, medical and dental history. Probing depth (PD) ? 4mm presented at 9% of sites in case and 4% of sites in control. There was 7% of sites in case and 3% of sites in control with CAL? 3mm. Periodontitis was diagnosed in 33.9% of the cases and 10.4% of the controls. Periodontitis was significantly associated with preterm birth (adjusted OR = 4.47, 95%CI= 2.43,8.20). These findings suggest that periodontitis may increase the risk of preterm birth even among women who do not smoke or drink.