This study reported outcomes of 31 recurrent or metastatic head and neck squamous cell carcinoma (HNSCC) patients treated with combined proton therapy and durvalumab plus tremelimumab. Proton therapy was given with a total dose of 25 Gy in 5 Gy daily fractions to one of the measurable lesions. With 8.6 months of follow-up, the objective response rate (ORR) was 22.6% (7/31), including one complete response and six partial responses. The median OS was 8.4 months and the median PFS was 2.4 months. Among the 23 evaluable patients who completed proton therapy, the ORR was 30.4% (7/23); the median OS was 11.1 months and the median PFS was 3.7 months. Grade 3 or higher adverse events were observed in six patients (19.4%).