The administration of ketamine as nebulized inhalation is relatively new and studies on nebulized ketamine are scarce. We aimed to investigate the analgesic efficacy of nebulized ketamine (1 and 2 mg.kg−1) administered 30 min before general anesthesia in children undergoing elective tonsillectomy in comparison with intravenous ketamine (0.5 mg.kg−1) and saline placebo. Methods: One hundred children aged (7-12) years were randomly allocated in four groups) n = 25) receive; Saline Placebo (Group C), Intravenous Ketamine 0.5 mg.kg−1 (Group K-IV), Nebulized Ketamine 1 mg.kg−1 (Group K-N1) or 2 mg.kg−1 (Group K-N2). The primary endpoint was the total consumption of rescue analgesics in the first 24 h postoperative. Results: The mean time to first request for rescue analgesics was prolonged in K-N1(400.9±60.5 min, 95% CI 375.9-425.87) and K-N2 (455. 5±44.6 min, 95% CI 437.1-473.9) groups compared with Group K-IV (318.5±86.1 min, 95% CI 282.9-354.1) and Group C (68.3±21.9 min, 95% CI 59.5-77.1; p 0.001), with a significant difference between K-N1 and K-N2 Groups(p 0.001). The total consumption of IV paracetamol in the first 24 h postoperative was reduced in Group K-IV (672.6±272.8 mg, 95% CI 559.9---785.2), Group K-N1 (715.6± 103.2 mg, 95% CI 590.4-840.8) and Group K-N2 (696.6±133.3 mg, 95% CI 558.8-834.4) compared with Control Group (1153.8±312.4 mg, 95% CI 1024.8-1282.8; p 0.001). With no difference between intravenous and Nebulized Ketamine Groups (p = 0.312). Patients in intravenous and Nebulized Ketamine Groups showed lower postoperative VRS scores compared with Group C (p 0.001), no differences between K-IV, K-N1 or K-N2 group and without significant adverse effects Conclusion: Preemptive nebulized ketamine was effective for post-tonsillectomy pain relief. It can be considered as an effective alternative route to IV ketamine.