Background: Spondylolisthesis, a prevalent source of low back pain, may require surgery after conservative treatment. Techniques like PLIF, ALIF, and TLIF have distinct benefits; PLIF, notably, provides stabilization and sagittal balance restoration via a single posterior approach. Objective: This study aimed to assess the outcomes of Lumbar Interbody Fusion and Posterior Instrumentation in Spondylolisthesis using cages and bone grafts. The study evaluated the impact of lumbar decompression, interbody fusion, and stabilization on patients' conditions. Methods: A prospective observational study was conducted at Dhaka Medical College Hospital from January to December 2021, involving 21 patients who underwent the operative procedure. The analysis encompassed the influence of lumbar decompression, interbody fusion using bone graft with cages, and stabilization with pedicle screws and rods on lumbar Spondylolisthesis patients. Results: Out of 21 patients, 7(33.3%) were male and 14(66.7%) were female. The mean age was 46.90±13.7 years and range between 23-70 years. The most expected involved level is L4 overL57(81.0%). According to Meyerding's grading, grade II was 15(71.4%), and grade I was 6 (28.6%), according to types ofSpondylolistheses lytic 12(57.1%), degenerative 8(38.1%), and dysplastic 1 (4.8%). Excellent outcomes were seen in 17(81.0%) cases and good results were found in 4(19.0%) cases. Probably not fused after surgery was observed in 2(9.5%) patients. The preoperative Oswestry Disability Index was 57.78±2.25, and the postoperative ODI was 16.56±3.53. Conclusion: Instrumented fusion demonstrated higher fusion rates and superior clinical outcomes, suggesting its efficacy in managing lumbar spondylolisthesis.