This study aims to demonstrate the surgical technique of inserting a larger cage, typically used in the oblique lateral interbody fusion (OLIF) approach, through the unilateral biportal endoscopic trans-Kambin triangle lumbar interbody fusion (UBE-KLIF) method to maximize the cage footprint and increase fusion rates with minimal tissue disruption. UBE-KLIF is a minimally invasive alternative to traditional open and other fusion methods, and it is particularly suitable for patients without central spinal stenosis where decompression is unnecessary. In this case, a 68-year-old woman with L4–5 spondylolisthesis and instability, presenting with low back pain radiating to her left lower limb, was treated using the UBE-KLIF approach. A large OLIF cage (50 mm×18 mm×10 mm) was successfully inserted, achieving an endplate-to-cage footprint ratio of 46.8%. The procedure minimized tissue disruption while enabling the use of a larger cage, which could potentially improve the fusion rate. This technique demonstrates the feasibility and effectiveness of inserting a larger OLIF cage via the UBE-KLIF approach in patients without central stenosis, offering a promising minimally invasive option for improving fusion outcomes.