Aims: Posterior lumbar interbody fusion (PLIF) is frequently used to treat spinal instabilities that can cause neurological symptoms, leg pain and low back pain including lumbar stenosis, degenerative disc disease and spondylolisthesis in which one vertebra slips over another. This study aimed to compare the clinical and radiographic outcomes of PLIF for degenerative L4 unstable grade III spondylolisthesis using bone grafts and cage bone grafts. Methods: Between from September 2021 to August 2023, 30 patients with degenerative lumbar spine disorders were selected based on the inclusion and exclusion criteria for PLIF. Results: We enrolled 30 patients and divided them into 15 groups (bone graft group I and Cage bone graft group II). The follow-up period was 2 years. Low back pain and leg function of the Japanese Orthopaedic Association (JOA) score showed significant improvement (p <0.005) at 3 months and at the final postoperative (62.1±5.5, 602±5.1) in both groups. The fusion rate was 93% in group I and 83% in group II. Radiological evaluation showed significant changes in slip angle, disc height, lumbar lordosis and translational motion from preoperative to final follow-up in both groups. A computer tomography (CT) revealed bilateral spondylolysis, disc collapse and anterolisthesis of the fifth lumbar vertebra. These results were verified by magnetic resonance imaging (MRI). There was no spinal canal stenosis. Conclusion: This finding suggests that successful clinical and radiological results can be obtained with PLIF surgery using either a cage with bone or a bone graft alone. The surgeon's inclination, the particular state of the patient and the resources at hand may influence which of the two approaches is used. The results showed no statistically significant difference between the two groups in terms of clinical and radiological outcomes (bone graft and cage with bone graft). This indicates that neither strategy showed a clear edge over the others in the criteria under study and both were equally successful in yielding favorable outcomes.