Objective To investigate the safety and effectiveness of unilateral biportal endoscopy (UBE) technique in the treatment of single-segment thoracic ossification of ligamentum flavum (TOLF). Methods Between August 2020 and December 2021, 11 patients with single-segment TOLF were treated with UBE technique. There were 6 males and 5 females, with an average of 58.2 years (range, 49-72 years). The responsible segment was T6, 7 in 1 case, T7, 8 in 1 case, T8, 9 in 2 cases, T9, 10 in 2 cases, T10, 11 in 2 cases, and T11, 12 in 3 cases. Imaging examination showed that the ossification were located on the left side in 4 cases, on the right side in 3 cases, and on bilateral sides in 4 cases. The main clinical symptoms were chest and back pain or lower limb pain, all accompanied by lower limb numbness and fatigue. The disease duration ranged from 2 to 28 months (median, 17 months). The operation time, postoperative hospital stay, and complications were recorded. Visual analogue scale (VAS) score was used to evaluate the chest and back pain and low limb pain, and Oswestry disability index (ODI) and Japanese Orthopedic Association (JOA) score were used to evaluate functional recovery before operation and at 3 days, 1 month, 3 months after operation, and last follow-up. The anteroposterior diameter of the coronal spinal canal was measured by CT before and after operation to evaluate the effect of surgical decompression. Results All operations were successfully completed. The operation time was 50-105 minutes, with an average of 80.0 minutes. No postoperative complication such as dural sac tear, cerebrospinal fluid leakage, spinal nerve injury, or infection occurred. The postoperative hospital stay was 2-5 days, with an average of 3.1 days. All incisions healed by first intention. All patients were followed up 6-22 months, with an average of 14.8 months. CT measurement at 3 days after operation showed that the anteroposterior diameter of the spinal canal was (8.63±1.61) mm, which was significantly larger than that before operation [(3.67±1.37) mm] (t=−12.181, P<0.001). The VAS score of chest and back pain and lower limb pain and ODI at each time point after operation were significantly lower than those before operation (P<0.05). The above indexes were further improved after operation, except that there was no significant difference between at 3 months after operation and at last follow-up (P>0.05), the differences between other time points were significant (P<0.05). There was no recurrence during the follow-up period. Conclusion UBE technique is a safe and effective method to treat single-segment TOLF, but its long-term effectiveness needs to be further studied.