This study compared clinical outcomes and learning curves between full-endoscopic spine surgery (FESS) and biportal endoscopic spine surgery (BESS) for interlaminar lumbar decompression performed by a single surgeon with extensive microscopic/endoscopic lumbar surgery (MEL) experience (>300 cases). We retrospectively analyzed single-level lumbar spinal stenosis cases treated between 2018 and 2024, excluding herniotomy cases and those with <3 months follow-up. Operative time, complications, reoperations, VAS scores, JOA scores, and JOA recovery rates were evaluated. Learning curves were assessed using linear regression of operative time against case sequence, adjusted for age, BMI, and surgical level. Eighty-seven cases were included (FESS: 41; BESS: 46). Baseline characteristics were comparable except for slightly younger age in the BESS group. Median operative time was significantly shorter in the BESS group (47.5 vs. 96.5 minutes, p<0.001). Both groups demonstrated significant improvements in JOA and VAS scores at 3 months with comparable recovery rates (55.3% vs. 56.7%). Complication and reoperation rates were similar between groups. Learning curve analysis showed stable operative times in FESS and an early downward trend in BESS, with both techniques reaching a plateau within the initial phase of adoption. Both FESS and BESS provided comparable clinical improvement. BESS achieved significantly shorter operative times and demonstrated rapid procedural stabilization. These findings suggest that surgeons with substantial MEL experience can transition to BESS without a prolonged learning curve while maintaining equivalent clinical outcomes.