The erector spinae plane block (ESPB) is gaining popularity in lumbar fusion for postoperative pain management. The aim of this study was to investigate the changes of opioid consumption after surgery, the range of cold temperature sensory blockade, pain, and safety. Randomized controlled study. Single center. Patients who were randomized to ESPB with 0.375% ropivacaine (ropivacaine group) and mock ESPB with saline (saline group) and underwent posterior lumbar fusion surgery. The primary endpoint was the total dosage of oxycodone. Secondary endpoints included remifentanil consumption, postoperative pain scores, postoperative adverse events, safety, and range of cold hypoesthesia. Oxycodone consumption in the first 48 hours after surgery was significantly lower in the ropivacaine group than in the saline group (P < 0.05). Remifentanil consumption was significantly lower in the ropivacaine group compared with the saline group during the surgery (0.69 ± 0.03 mg vs. 0.85 ± 0.04 mg, P < 0.05). The areas of cold hypoesthesia were identified in the ropivacaine group after the block, but not in the saline group. Rest and exercise pain scores after surgery were significantly lower in the ropivacaine group than in the saline group (P < 0.05). The overall safety of the ropivacaine group were generally comparable to that of the saline group. The areas of cold hypoesthesia were tested at different time points after ESPB, but the area of sensory loss was not tested, and the recovery of postoperative sensation was not recorded. In addition, we tested only temperature sensation, but not acupuncture pain. Ultrasound-guided lumbar ESPB reduces the amount of analgesics required during and after lumbar fusion and reduces the postoperative Visual Analog Scale pain score.