Background: A standard obstetric analgesic should have a good analgesic effect without reducing the intensity of uterine contraction. The present study aimed to evaluate and compare the efficacy of intramuscular tramadol and pethidine on labor pain and duration. Material and Methods: A total of 170 multigravida women in active labor were randomly assigned to two identical groups, so that 85 pregnant women received pethidine (50mg/2ml) and 85 pregnant women received tramadol (100mg/2ml) intramuscularly. Results: The labor duration in the tramadol group was shorter than in the pethidine group. In 1st stage of labor, 64.7% of the participants in the tramadol group received the drug for 120±30 minutes, while 67.1% in the pethidine group received the drug for 180±30 minutes. In the 2nd stage, 44.7% of the participants in the tramadol group received the drug for 15±5 minutes, while 51.8% in the pethidine group received the drug for 25±5 minutes. The Visual Analog Scale (VAS) was used before, and 1 and 3 hours after drug administration. The pethidine group obtained a lower VAS mean score compared to those in the tramadol group at 1 hour after drug administration (4 vs 6; P≤.001). Moreover, there was a significant higher level of vomiting and dizziness among women in the pethidine group (29.4% vs 1.2%; P≤.001). Conclusion: Tramadol appears to lead to a shorter labor duration and cause lower maternal side-effects, although its analgesic efficacy was not as much as pethidine.