Abstract:[Objective] To introduce the surgical technique and preliminary clinical results of closed osteotomy by fracture line through posterior approach for ankylosing spondylitis stress fracture. [Methods] From January 2010 to June 2016, 16 patients with ankylosing spon- dylitis complicated with thoracolumbar stress fracture were treated by the above surgical procedures. A posterior midline incision was made to expose the fractured vertebra bilaterally to the anterior part, and then 2~3 pairs of pedicle screws were placed respectively on the seg- ments superior and inferior to the affected vertebra. After the corresponding lamina and facet process were removed, the fracture space on the vertebral body was identified and debrided, then a V-shaped osteotomy was performed beside the fracture line, followed by bone auto- graft or allograft implanted into the osteotomy space. Placing bilateral rods, the screw-rod systems were adjusted to close the osteotomy gap, eventually were fastened definitively. [Results] All the 16 patients had the operations performed successfully. Except one patient who was suffered from significant muscle weakness postoperatively, which well recovered 4 months later by rehabilitation, all the patients had no se- rious complications. The VAS and ODI scores significantly decreased at the latest follow-up compared with those before surgery (P＜0.05) . Radiographically, the thoracic kyphosis, global kyphosis, angle of the fusion levels, local kyphosis and sagittal vertical axis significantly im- proved at the latest follow-up compared with those preoperatively (P＜0.05) . Bony fusion achieved at all osteotomy sites without loosening of internal fixators. [Conclusion] This closed osteotomy by fracture line through posterior approach has benefits of complete debridement of the lesion between the fracture ends, obvious pain relief and effective correction of the deformity, is facilitated to fracture healing with high safety.