Introduction: Vertebral slip reduction has been recommended in arthrodesis for lumbar degenerative spondylolisthesis (LDS) to achieve balanced spinal alignment and bone fusion. However, what determines the degree of slip reduction using cortical bone trajectory technique for lumbar pedicle screw insertion is yet to be determined. Thus, in this study, we aim to investigate the slip reduction capacity using cortical bone trajectory (CBT) technique and to identify factors affecting the slip reduction rate. Methods: This is a retrospective radiological evaluation of prospectively collected patients. In total, 49 consecutive patients who underwent single-level transforaminal lumbar interbody fusion for LDS using the CBT technique were included (mean follow-up: 28.9 months). Firstly, radiological parameters of fused segment including the percentage of anterior vertebral slip (%slip), lordotic angle, and disk height were measured. Then, patient and procedure-related parameters were examined to determine factors related to the slip reduction rate using multiple regression analysis. Results: The %slip was reduced from 15.0±4.8 to 1.6±2.3% immediately after surgery and 2.2±2.9% at the last follow-up (p