Background: The current study aimed at investigating the effect of using entonox gas during sedation and analgesia induction in pediatric candidates of bone marrow aspiration. Methods: It was a single-blind, randomized clinical trial. All pediatric candidates of 1st time bone marrow aspiration were included and allocated to either group 1 or 2, using a random number table. In group 1, a combination of midazolam, fentanyl, ketamine, and propofol was injected intravenously. In group 2, the mentioned combination was injected intravenously and entonox gas was used for patients' ventilation. The goal was to reach level 4 sedation based on the Ramsay sedation scale. If needed, extra propofol was injected intravenously every minute. Physician and the helping nurse satisfaction of the procedure were evaluated. Duration of the procedure, the administered dosage for each patient, occurrence of any complications, and the recovery time were recorded.