Background: Poor perioperative pain management during pneumothorax surgery leads to respiratory complications in the post-operative period. The erector spinae plane (ESP) block technique has been shown to be able to block the thoracic spinal nerves. Therefore, the ESP block may provide effective analgesic during thoracic surgery. We have retrospectively investigated the effectiveness of the ESP block for postoperative pain management in pneumothorax surgery. Patients and Methods: Patients who underwent pneumothorax surgery in 2017 were selected for the study. The primary outcome was assessed using the numeric pain rating (NRS) scales until the morning of the second post-operative day. The secondary outcomes were the cumulative amount of additional intravenous fentanyl administration until the morning of the second post-operative day. Results: This retrospective study included 29 patients who underwent pneumothorax surgery. Of these patients, 13 patients received only general anaesthesia (control group), while the other 16 patients received the ESP block in addition to general anaesthesia (study group). Compared to the control group, the study group did not show lower NRS scores at 1, 2, 4, 6, 12, and 24 hours post-surgery (P = 0.09, 0.17, 0.06, 0.36, 0.47, and 0.71). As for the cumulative amount of additional fentanyl, there were also no significant differences between the both groups. Conclusions: The ESP block could not provide effective analgesia for the 24 hours post-surgery period in patients undergoing pneumothorax surgery.