목적: This study evaluated the prognostic significance of the margin-to-depth of invasion ratio (MDR) in patients with oral squamous cell carcinoma (OSCC) treated with surgery and adjuvant concurrent chemoradiotherapy (CCRT). 방법:A cohort of 452 OSCC patients who underwent radical surgery followed by adjuvant CCRT between 2007 and 2017 was analyzed. Cox proportional hazards models were employed to assess factors associated with cancer-specific survival (CSS) and relapse-free survival (RFS). 결과:The optimal MDR cutoff was determined as 0.35. Patients with MDR 0.35 had significantly better 5-year CSS (76% vs. 56.7%, p<0.001) and RFS (70.6% vs. 53.4%, p=0.001) compared to those with MDR <0.35. Multivariate analysis identified low MDR as an independent negative predictor of CSS (HR: 2.343, 95% CI: 1.6573.313, p<0.001) and RFS (HR: 1.789, 95% CI: 1.3192.426, p<0.001). Among patients with a surgical margin greater than or equal to 5 mm, those with low MDR demonstrated significantly poorer CSS (p=0.002) and RFS (p=0.014) compared to high MDR counterparts. 결론:MDR was observed to determine the survival outcome for OSCC patients treated with surgery and adjuvant CCRT. Novel intensified treatment strategies are warranted for patients with low MDR, even if adequate surgical margins are achieved.