Abstract:[Objective] To evaluate the clinical outcomes of 3D printing assisted osteotomy and instrumented correction of kyphosis sec- ondary to ankylosing spondylitis (AS) . [Methods] A retrospective study was done on 47 patients who received surgical correction of kyphosis secondary to AS kyphosis in our hospital from December 2015 to December 2020. According to the results of doctor-patient communication, 19 patients underwent 3D print- assisted surgery (3D group) , and 28 patients underwent conventional freehand surgery (conventional group) . The documents regarding to perioperative period, follow-up and radiographs were compared between the two groups. [Results] All patients in both groups had operation finished successfully without death, paraplegia and other serious complications. The 3D group proved significantly superior to the conventional group in terms of operation time, total incision length, intraoperative blood loss, intraoperative fluo- roscopy times, amount of allogenic blood transfusion, postoperative hemoglobin (Hb) at 2 days, and hospital stay (P<0.05) , nevertheless there was no significant difference in incision healing grade between the two groups (P>0.05) . All of them in both groups were followed up for (27.7±3.3) months, and the 3D group returned to full weight-bearing activity significantly earlier than the conventional group (P<0.05) . The ADL, VAS, ODI and JOA scores improved significantly over time in both groups (P<0.05) , which in the 3D group were significantly better than those in the conventional group at 3 months and the latest follow- up (P<0.05) . Regarding imaging, the accuracy of pedicle screw placement in the 3D group was significantly better than that in the conventional group (P<0.05) . The Cobb angles of the main curva- ture and balance deviations in both sagittal and coronal planes significantly improved at 3 months and the last follow-up in both groups com- pared with those preoperatively (P<0.05) , which in the 3D group were significantly better than those in the conventional group at 3 months and the latest follow-up (P<0.05) . [Conclusion] The 3D printing assisted osteotomy and instrumented correction of kyphosis secondary to ankylosing spondylitis do significantly improve the accuracy of screw placement, shorten operation time, reduce surgical trauma and improve clinical outcome.