Purpose Tonsillectomy is still one of the most common surgical procedures worldwide performed by otorhinolaryngologists. This single-blind randomized study aimed to compare cold dissection tonsillectomy, coblation tonsillectomy, and harmonic scalpel tonsillectomy in pediatric patients in respect of intraoperative blood loss, operating time, and postoperative pain and bleeding. Methods This single-blind randomized clinical trial evaluated 82 pediatric patients aged 3-16 years (mean age: 7.23 +/- 3.26 years) applied with tonsillectomy between April 2017 and March 2020. Harmonic scalpel tonsillectomy was applied to 33 (40.2%) patients, the cold knife technique to 25 (30.5%), and coblation tonsillectomy to 24 (29.3%). Results There was no statistically significant difference between the three techniques in respect of postoperative pain levels and post-tonsillectomy bleeding rates. The intraoperative bleeding rate and mean operating time were determined to be significantly lower in the harmonic scalpel group (p < 0.05). Conclusion Harmonic scalpel tonsillectomy is associated with a shorter operating time and lower intraoperative bleeding rates and similar postoperative pain score and postoperative bleeding rates compared with coblation tonsillectomy and cold dissection tonsillectomy. Harmonic scalpel tonsillectomy is a fast, safe, and effective method for tonsillectomy in children.