Tonsillectomy is one of the most common head and neck surgeries worldwide. This surgery can cause severe and prolonged pain, and pain control after the operation is often not desirable. This study investigated the effect of peritonsillar dexmedetomidine injection on reducing pain after tonsillectomy in children. In this double-blind clinical trial, 71 children aged 4-15 years who underwent tonsillectomy in Heshmatieh Hospital of Sabzevar were enrolled. Induction of anesthesia was performed with fentanyl (4 µg/kg), propofol (2 mg/kg) and atracurium (0.4 mg/kg). Intubation was performed after 3 min of preoxygenation with 100% oxygen. Anesthesia was maintained with 50% nitrous oxide and 50% oxygen with 1.2% isoflurane. Dexmedetomidine (1 µg/kg) in group A was injected into the peritonsillar submucosal tissue, and no intervention was performed in the control group. Surgery began 5 min after the injection. Hemodynamic changes were assessed before, during and after surgery, and pain intensity was recorded at 4, 8, and 12 h after surgery. The duration of anesthesia was not significantly different between the two groups, but the recovery period was significantly longer in the intervention group. The pain intensity at 4, 8 and 12 h after surgery was significantly lower in the dexmedetomidine group than in the control group. In the dexmedetomidine group, the heart rate and blood pressure were lower than those in control group, but the oxygen saturation was greater than that in control group. Dexmedetomidine peritonsillar injection is safe and effective in reducing pain after tonsillectomy in children.