Metronomic chemotherapy inhibits tumor growth by continuous administration of lower-dose chemotherapy. Our study aimed to demonstrate the outcomes of metronomic chemotherapy with tegafur–uracil in locally advanced head and neck squamous cell carcinoma (LA HNSCC). This was a retrospective study including 240 patients with LA HNSCC. After standard treatment, 96 patients were further treated with metronomic tegafur-uracil, and 144 patients were not. No statistical differences were found between both groups with regard to sex, clinical stage, or primary treatment choice. There were more hypopharyngeal cancers and more patients with poor clinicopathological features, including lymphovascular invasion, extranodal extension, and positive margins in the tegafur–uracil group. The median follow-up duration was 31.16 months. Overall survival (OS) was not reached in the tegafur–uracil group and was 54.1 months in the control group (p = 0.008). The median disease-free survival (DFS) was 54.5 months in the tegafur–uracil group and 34.4 months in the control group (p = 0.03). Neither group reached distant metastasis-free survival (DMFS, p = 0.02). In patients with LA HNSCC, adding tegafur–uracil as metronomic chemotherapy after either curative surgery with adjuvant chemoradiotherapy or definitive concurrent chemoradiotherapy significantly improved the OS, DFS, and DMFS with tolerable adverse events.