Background: Pain is one of the main side effects of tonsillectomy, especially in the pediatric population. Objectives: This study aimed to examine the effects of a local injection of bupivacaine on pain and postoperative nausea and vomiting after tonsillectomy. Methods: In this double-blind clinical trial, we enrolled 96 patients who were referred for elective tonsillectomy to the ear, nose, and throat (ENT) Clinic of Imam Khomeini Hospital in Ahvaz, Iran, from December 2016 to January 2018. The patients were selected by the simple random sampling method on a 1:1 ratio. To analyze the data, Student's t‐test or chi‐squared test were used. Results: Visual analog score measured in the recovery period at 0, 1, 2, 4, 8, 12, and 24 h after surgery was significantly lower in the Bupivacaine group than in the Placebo group (P < 0.001). Nausea was significantly different between the groups at all time, but for vomiting, significant differences between the groups were noted at 0, 1, 2, 4, and 8 h but not at 12 and 24 h after surgery. Conclusions: Preoperative local injection of 0.5% bupivacaine for tonsillectomy was effective in reducing postoperative pain, and it significantly reduces postoperative nausea and vomiting in children.