The aim of this study was to evaluate the synergistic potentiation effect of ineffective doses of dexmedetomidine on antinociception induced by morphine and fentanyl in acute pain model in rats. Seventy albino Wistar rats were separated into 7 groups. Data for the control and sham groups were recorded. The ineffective dose of dexmedetomidine was investigated and found to be 3 mu g/kg. Each group was administered the following medications: 3 mg/kg morphine (intraperitoneal) to Group 3, 5 mu g/kg fentanyl (intraperitoneal) to Group 4, dexmedetomidine 3 mu g/kg (subcutaneously) to Group 5, dexmedetomidine 3 mu g/kg (subcutaneous)+3 mg/kg morphine (intraperitoneal) to Group 6 and finally 3 mu g/kg dexmedetomidine (subcutaneous)+5 mu g/kg fentanyl (intraperitoneal) to Group 7. Just before the application and 15, 30, 60, 90 and 120 min after the administration of medication, two measurements of tail flick (TF) and hot plate (HP) tests were performed. The averages of the measurements were recorded. TF and HP latencies were the main outcomes. The analgesic effect of the combinations with dexmedetomidine+morphine (Group 6) and dexmedetomidine+fentanyl (Group 7), compared to the analgesic effect of morphine alone and fentanyl alone was significantly higher at 15, 30, 60 and 90 minutes after administration. In this study, dexmedetomidine in ineffective doses, when combined with morphine and fentanyl, potentiates the effects of both morphine and fentanyl.