Background: Induction of analgesia is frequently required during undergoing reduction of fractures or dislocation in the emergency department. Method to induce analgesia should be easy, convenient, and safe because patients are not always in fasting state. Nitrous oxide inhalation has been known as a good method of analgesia in emergency patients. Purpose: This study was aimed to evaluate the efficacy and safety of nitrous oxide analgesia in the emergency department. Method: We prospectively studied 34 patients undergone reductions of fractures in the emergency department. Nitrous-oxide was the sole source of analgesia. The Visual Analogue Scale(VAS) was rated by the emergency physician before nitrous oxide inhalation, 5 minutes after inhalation and reduction procedures. Results: No complication such as vomiting, respiratory depression, or a change in oxygen saturation resulted from the use of nitrous-oxide. Ninety one percent of patients obtained an analgesic effect. However, 9% of patients did not experience any analgesic effect after inhalation of nitrous oxide. In subgroup analysis for analgesic effect of nitrous- oxide, nitrous oxide provided only partial analgesia for acute pain in open fracture group. VAS was significantly lower after inhalation than before inhalation of nitrous oxide in simple fracture group. However, VAS of simple fracture group was increased during closed reductions, which indicated incomplete relief of pain by nitrous oxide. Nitrous oxide inhalation failed to relieve pain during reduction in patients with open fracture or dislocation. Conclusion: Administration of nitrous-oxide, when used as the sole source of analgesia, is not the ideal method of analgesia during reduction of fractures or dislocations.