Introduction: Surgical ligation for hemodynamically significant patent ductus arteriosus (PDA) is sometimes required in preterm infants; however, some patients experience worsened respiratory status after the surgery. This study aimed to evaluate the risk factors that could predict worsened respiratory outcomes after PDA ligation. Methods: A retrospective cohort study was performed on 57 preterm infants born at less than 32 weeks of gestational age and in whom the PDA was surgically ligated between January 2014 and December 2018 at Seoul National University Children’s Hospital. Participants were divided into two groups: infants with worsened respiratory outcomes 14 days after ligation and control. Worsened respiratory outcome was defined as increase in respiratory severity score (RSS) by 30% or more at 14 days after ligation compared to RSS before ligation, or death at 14 days after ligation. Results: Among the 57 PDA-ligated infants, 12 had worsened respiratory outcomes and 45 did not. The worsened respiratory outcomes were associated with oligohydramnios (adjusted OR 1.373, 95% CI 1.113-1.694.), histologic chorioamnionitis (adjusted OR 1.240, 95% CI 1.016-1.512), and decreased weight on the day of surgery (adjusted OR 0.999, 95% CI 0.999-0.999) compared to that in the control. Conclusion: Worsened respiratory outcomes after PDA ligation appeared to be associated with oligohydramnios, histologic chorioamnionitis, and weight on the day of surgery.