To evaluate the safety, effect on breastfeeding and efficacy of a combination of pethidine and levallorphan (Pethilorfan) for pain relief during labor.We compared maternal or neonatal morbidities, suckling difficulties in newborns and breastfeeding rates between 177 women who received 50-200 mg (as pethidine) of Pethilorfan during labor (Pethilorfan group) and 354 women who delivered their infants without analgesic drugs immediately before or after each woman in the Pethilorfan group (control group) from January 1, 2005 to December 31, 2016. We performed univariate and multivariate analyses for comparison between the two groups. We also evaluated the efficacy of Pethilorfan retrospectively.The Pethilorfan group included more women with prolonged and/or operative deliveries than the control group. Nevertheless, no significant differences were seen between the two groups in the rates of Apgar scores less than 7 at 1 or 5 min, composite neonatal morbidities, hyperbilirubinemia or respiratory disturbances. The incidence of suckling difficulties lasting over 24 h and the breastfeeding rates at discharge or after 1 month were also similar. Maternal adverse effects of Pethilorfan were generally mild and transient. The efficacy ratio of Pethilorfan was 83.6%, although its analgesic effect was usually incomplete.Pethilorfan can be used safely for labor pain relief without increasing maternal or neonatal morbidities, or impeding breastfeeding, if it is administered at a prudent dosage. Parenteral opioids including Pethilorfan should remain as an option for treating women in labor pain, particularly when epidural analgesia is not readily available or contraindicated.