Abstract:[Objective] To compare the clinical outcomes of posterior lumbar interbody fusion (PLIF) with or without preservation of the spinous process -ligament complex in the treatment of lumbar instability. [Methods] A retrospective study was conducted on a total of 84 pa- tients who received PLIF for lumbar instability in our hospital from February 2017 to December 2020. According to the results of preopera- tive doctor-patient communication, 42 patients had the spinous process-ligament complex preserved, while the remaining 42 patients had the spinous process-ligament complex removed routinely. The documents regarding to perioperative period, follow-up and radiographs were compared between the two groups. [Results] All patients in both groups had operation done successfully without serious complications. The preserved group proved significantly superior to the removed group in terms of intraoperative blood loss, postoperative drainage volume and VAS score of postoperative incision pain (P<0.05) , although there was no significant difference in operation time and hospital stay between the two groups (P>0.05) . The VAS scores of the low back pain and leg pain, ODI and JOA scores significantly improved in both groups over time (P<0.05) . At latest follow-up, the preserved group was significantly superior to the removed group in VAS score of low back pain and JOA score (P<0.05) , but there was no significant difference in VAS score of leg pain between the two groups (P>0.05) . During the followup, postoperative persistent syndrome (POPS) did not occur in anyone of the preserved group, while which was of 8/42 (19.05%) in the re- moved group, with a statistically significant difference (P<0.001) . Radiographically, the lumbar lordosis angle, intervertebral space height, and slippage percentage significantly improved in both groups at the latest follow-up compared with those before operation (P<0.05) , addi- tionally, the Lenke fusion grade improved significantly over time in both groups (P<0.05) . At the corresponding time points, there was no sig- nificant difference in the above imaging indexes between the two groups (P>0.05) . [Conclusion] PLIFs with or without spinous process-lig-ament complex preservation are effective treatment of lumbar instability. By comparison, preservation of the complex is benefit to improve the long-term outcome.