Objectives: This trial aimed to ascertain the relative efficacy, adverse effects, and acceptability of fentanyl versus pethidine for pain relief during labour. Materials and Methods: Parturients (n=80) in the active phase who requested analgesia were randomly assigned to receive either intravenous fentanyl (n=40) or intramuscular pethidine (n=40). Pain scores hourly, maternal and fetal adverse effects, neonatal outcome, and maternal acceptability were assessed. Results: Pain scores decreased in both groups, the decrease varying from mild to moderate, average pain scores remaining above 3.5 in both groups. Pain scores returned towards baseline over time; three hours after the initiation of treatment in the fentanyl group. Pethidine was associated with more maternal nausea and vomiting (p < 0.05) while fentanyl was associated with more neonates with low Apgar scores at one minute and more need for neonatal resuscitation and naloxone administration when compared to pethidine (p < 0.05). Both drugs were acceptable for pain relief during labour. Conclusion: Fentanyl is comparable to pethidine for pain relief during labour regarding efficacy and acceptability, but with more neonates with low Apgar scores at one minute and higher need for neonatal resuscitation and naloxone administration. Further larger trials are needed to confirm its safety.