Purpose To investigate the perioperative outcomes, clinical manifestations, and radiographic indicators in patients who underwent oblique lateral lumbar fusion (OLIF) and posterior instrumentation, compared with those who underwent posterior transforaminal lumbar interbody fusion (TLIF) and instrumentation. Methods In this retrospective cohort analysis, elderly patients diagnosed with L4-5 lumbar spinal stenosis between July 2022 and July 2023 at our institution who underwent OLIF and posterior instrumentation (OLIF group), compared with those who underwent posterior TLIF and instrumentation (TLIF group). Enhanced Recovery After Surgery (ERAS) protocol was implemented for all patients. The perioperative data, patient-reported outcomes (PROs), radiographic assessments, and complications were gathered immediately after surgery and again at the 1-year follow-up. The perioperative outcomes and immediately postoperative and follow-up radiographic outcomes were compared between the two groups. Results A total of 120 patients participated in this study, with 60 patients assigned to the OLIF group and 60 to the TLIF group. With respect to outcomes, the length of stay was notably shorter in the OLIF group compared to the TLIF group (P < 0.001). Patients in the OLIF group exhibited significantly reduced postoperative drainage volume (P < 0.001), first ambulation on the postoperative day (POD) (P < 0.001), drain placement duration (P < 0.001), and urinary catheter retention (P = 0.037) compared to those in the TLIF group. Furthermore, there were statistically significant differences between the two groups in the incidence of postoperative deep venous thrombosis (DVT) (1 vs. 8, P = 0.015), urinary tract infection (2 vs. 11, P = 0.008), pulmonary infection (2 vs. 10, P = 0.015), and nausea and vomiting (3 vs. 11, P = 0.023). With respect to radiographic measurements, At the 1-year follow-up, the posterior disc height (PDH) and intervertebral disc angle (IDA) demonstrated statistically increase in the OLIF group. The sagittal vertical axis (SVA) was statistically decrease and Lumbosacral lordosis (LL) was statistically increase in the OLIF group. Conclusion OLIF was demonstrated to have significant advantages in terms of perioperative, clinical outcomes and radiographic parameters for L4-5 lumbar spinal stenosis for elderly patients, comapred with TLIF.