Posterior spinal fusion for adolescent idiopathic scoliosis (AIS) causes severe postoperative pain. Thoracic paravertebral block (PVB) provides excellent analgesia during various surgeries. We examined the effects of PVB on postoperative analgesia in children undergoing AIS surgery. In this study, 32 children scheduled for AIS surgery were randomly assigned to receive either PVB (PVB group) or no block (control group). The PVB group underwent surgeon-performed PVB with 0.5 mL/kg of adrenalized 0.2% ropivacaine on each side. The primary outcome was the pain score at rest at 6 h postoperatively. Secondary outcomes included pain scores both at rest and during movement and analgesic use for 48 h postoperatively. The postoperative resting pain scores at 6 h were comparable between the control and PVB groups (5.2 ± 2.0 and 5.1 ± 1.8, respectively), with no significant differences. However, at 1 h postoperatively, the control group showed significantly higher resting and mean moving pain scores than the PVB group (p < 0.05). The pain scores at other time points and analgesic use were comparable between the groups. Initial benefits of surgeon-performed bilateral PVB were observed but diminished at 6 h postoperatively. Future research using various anesthetics is needed to extend the effects of PVB.