Abstract:[Objective] To introduce the surgical technique and preliminary clinical results of modified transforaminal approach for full endoscopic L5S1 decompression of foraminal stenosis. [Methods] A total of 12 patients with L5S1 foraminal stenosis were treated by modified foraminal approach with full endoscopic L5S1 decompression of foraminal stenosis. The horizontal line of the intervertebral foramina L5S1 on the affected side was taken as the puncture path, while the inside of the intersection of the horizontal line and the crest of the iliac crest was used as the puncture needle point. The puncture was carried out to the outside of the junction between the isthmus of L5 and the apex of the superior articular process of S1, and then the cannula was inserted, and the isthmus of L5 and a small part of the apex of the superior articular process of S1 were removed with an external circular saw under the all-visual endoscope. The protruding nucleus pulposus, hypertrophic ligamentum flavum, or calcified ligamentum flavum pressing on the L5 nerve root were removed to complete decompression of the L5 nerve root. [Results] All the patients had operation performed smoothly and got significant improvement in terms of symptoms and function, except 1 who had a tear of the outer nerve root membrane and another had postoperative hip pain, both of them had no serious adverse consequences. During the follow-up period lasted for 6 months to 5 years, no recurrence or worsening of symptoms was found in anyone of them. [Conclusion] Modified transforaminal approach full endoscopic decompression for the treatment of L5S1 foraminal stenosis has the advantages of strong repeatability, no restriction of high iliac crest, and no impact on spinal stability.