Abstract:[Objective] To explore the safety and effectiveness of 3D printed guider assisted pedicle screw placement in corrective oste- otomies for kyphotic deformity secondary to ankylosing spondylitis (AS) . [Methods] A retrospective analysis was performed on 70 patients who underwent surgical correction for kyphotic deformity secondary to AS in our hospital from June 2014 to December 2019. According to the preoperative doctor-patient communication results, 38 patients received corrective osteotomies with 3D printed guiders assisted pedicle screw placements (the 3D group) , while the other 32 patients underwent surgical procedures with pedicle screw placement with the conven- tional freehand technique (the freehand group) . The documentations regarding to perioperative conditions, follow-up indicators and imag- ing results were compared between the two groups. [Results] All the patients in both groups had operation performed successfully without serious complications. The 3D group proved significantly superior to the freehand group in terms of operation time, intraoperative blood loss, postoperative drainage, intraoperative X-ray frequency and hospital stay (P<0.05) . Although no complications, such as deep infection and symptomatic thrombosis, occurred in the two groups, incision hematoma was noted in 1 case of the 3D group and 2 cases of the free- hand group, while nerve root injury was seen in only 1 case of the freehand group, all of which were subsided after corresponding treatment. All patients were followed up for 12~43 months, with an average of (22.47±5.84) months. The 3D group resumed walking and full weightbearing activity significantly earlier than the freehand group (P<0.05) . The body height, sitting height and JOA scores significantly in- creased in both groups (P<0.05) , whereas the VAS and ODI scores significantly decreased in both groups at the latest follow-up compared with those before operation (P<0.05) . At the latest follow-up, the 3D group was significantly superior to the freehand group in abovemen- tioned items (P<0.05) . Radiographically, the 3D group got significantly better accuracy of screw placement than the freehand group (P< 0.05) . The sagittal kyphotic Cobb angle and the sagittal C7PL deviation significantly reduced in both groups postoperatively compared with those preoperatively (P<0.05) , which proved significantly better in the 3D group than the freehand group at the last follow-up (P<0.05) .[Conclusion] Application of 3D printed guider in corrective osteotomies for kyphotic deformity secondary to AS does significantly improve the efficiency and accuracy of screw placement, and improve the clinical results.