BackgroundPain control after surgery in children is very important. Despite having good analgesic effects, the use of opioids is, however, limited due to side effects.ObjectivesThis study was aimed to investigate the effect of transverse abdominis plane (TAP) block on the intensity and frequency of pain after appendectomy in children.MethodsIn a single-blinded clinical trial, 40 children aged from 4 to 16 years, candidates for the appendectomy, were divided randomly to intervention and control groups. The intervention group received ultrasound-guided TAP block using 0.25 mL/kg of 0.25% bupivacaine in the Petit triangle after general anesthesia. Postoperative pain was assessed within the first 24 hours after surgery based on the Wong-Baker FACES Pain Rating Scale (WBFP).ResultsThere was a reduction in WBFP scores at 2 hours after appendectomy in the intervention group compared with the control group (5.05 ± 2.83 vs 6.30 ± 2.2063). Also, the pain intensity within 24 hours after surgery in the intervention and control groups was 3.10 ± 1.33, and 3.60 ± 1.63 respectively according to WBFP scale (P > 0.05).ConclusionsThe TAP block was effective to reduce pain after appendectomy in children, however, there was no significant difference between intervention and control groups. Further studies with larger sample sizes are needed to be done in this area of research.