Background: morphine is a potent analgesic in decreasing postoperative pain; however its use is accompanied by many complications especially respiratory one. On the other side, fentanyl titration may cause less postoperative respiratory complications. Objective: To compare between intravenous long-acting opioid (Morphine), and short-acting opioid (Fentanyl) regarding postoperative hypoxemia after non-cardiac surgery. Patients and methods: A prospective randomized clinical study done on 52 patients, they were divided equally into two groups: Group M (Morphine) received (0.1mg/kg), and Group F (Fentanyl) received (1ug/kg) on induction, and supplemented by effective rescue analgesia. When postoperative VAS score ≥4 , patients in Group M received 5mg morphine as bolus ,and re-assess pain every 5 min to give another bolus ( the total allowed dose was 15mg/3-4h).For Group F 50ug fentanyl was given as a bolus ,and could be repeated (total allowed dose was 100 ug/1-2h.). Result(s): There were no significant difference between two groups as regard respiratory rate (RR) nor peripheral O2 saturation (SPO2) (P value0.05). Conclusion: Intravenous morphine as effective rescue analgesic is not associated with more postoperative hypoxemia, or respiratory depression than fentanyl