Background: Concurrent chemoradiotherapy (CCRT) with cisplatin (CDDP) is a standard treatment for locally advanced head and neck cancer (LAHNC) in the definitive setting. Three cycles of 100 mg/m² CDDP for every three weeks (Q3W) are now recommended but compliance with CCRT is relatively low due to its severe toxicity. Therefore, the potential de-escalation strategies for LAHNC have been discussed to decrease the therapeutic toxicity. Methods: Patients with LAHNC who underwent definitive CCRT with CDDP between 2012 and 2018 at The Cancer Institute Hospital of Japanese Foundation for Cancer Research were analyzed. Patients were classified into two groups based on the planned CDDP dose: (A) 100 mg/m² and (B) 80 mg/m² Q3W for three times. One-to-one propensity score matching was performed to minimize bias between two groups. After patients in two groups were matched by using propensity score, the overall survival (OS), recurrence-free survival (RFS), local recurrence-free survival (LRFS), and metastatic recurrence-free survival (MRFS) were analyzed by the Kaplan-Meier method with the Cox proportional hazards model. The follow-up term was set as two years to evaluate the early survival benefit. The dose and density of CDDP and the objective adverse events were also assessed. Results: A total of 304 patients were included with the median age of 62 (Interquartile range [IQR]: 54-67) years. Among them, 249 patients (82%) were male. Patients were treated with 100 mg/m² CDDP (n = 145) and 80 mg/m² CDDP (n = 159) regimens. After the propensity score matching, 119 patients were included in each group, respectively. There were no significant differences in baseline characteristics between two propensity-matched cohorts. The median follow-up time was 24 months in each group. Two-year OS was 93.0% (95% confidence interval [CI]: 88.4-97.8) in group A and 94.9% (91.0-99.0) in group B. Two-year RFS was 86.5% (80.6-92.9) in group A and 83.1% (76.6-90.1) in group B, respectively. No significant difference was observed in OS (Hazard ratio [HR] = 1.42, 95% CI: 0.49-4.08, p = 0.52), RFS (HR = 0.81, 95% CI: 0.42-1.57, p = 0.54), LRFS (HR = 0.57, 95% CI: 0.24-1.36, p = 0.20), and MFS (HR = 1.32, 95% CI: 0.52-3.35, p = 0.56). The median cumulative dose of CDDP was significantly higher in group A (300 mg, interquartile range [IQR]: 240-300) than in group B (240 mg, IQR:160-240) but the frequency of hematological, hepatic, renal, electrolytic, and grade 3-5 any adverse events was not significantly different between two groups. Conclusions: Our study showed no survival difference at 2-year follow-up between 100 mg/m² and 80 mg/m²CDDP regimens of definitive CCRT for LAHNC. This result could support the tide of the de-escalation strategy in head and neck cancer treatment. Longer follow-up is necessary and further prospective trials comparing CDDP dosage are warranted.