Background: The efficacy and safety of Pembrolizumab in recurrent /unresectable/metastatic head and neck squamous cell carcinoma have been well documented in KEYNOTE-048 and other studies, and the effectiveness of different areas’ population have been shown in related studies. However, there is no native data based on the Chinese population. The purpose of this study was to investigate the efficacy and safety of Pembrolizumab in the treatment of R/U/M head and neck squamous cell carcinoma in Chinese population. Methods: We reviewed patients data from the department of Oral & Maxillofacial Surgery, the Affiliated Hospital of Qingdao University. The patients with R/U/M head and neck squamous cell carcinoma were treated with or without combined chemotherapy / targeted therapy according to their PD-L1 expression status (CPS). Pembrolizumab was infused intravenously with 200mg every 3 weeks for a maximum of 35 cycles. The primary endpoint was Objective Response Rate(ORR). The secondary endpoints were Quality of Life, Safety and Progression Free Survival(PFS). Results: A total of 23 eligible patients with R/U/M head and neck squamous cell carcinoma were included from February 2021 to February 2022, including 18 males (78.26%) and 5 females (21.74%) with a median age of 68 years. The primary sites were oral cavity in 16 cases (69.56%), oropharynx in 4 cases (17.39%), hypopharynx in 1 case (4.35%), and larynx in 2 cases (8.70%). P16 status was positive in 4 cases (17.39%), negative in 12 cases (52.17%), and unknown in 7 cases (30.43%). The expression status of PD-L1 in all patients was known. Patients with CPS ≥ 20 were treated with Pembrolizumab monotherapy and patients with CPS < 20 were treated with Pembrolizumab combined with chemotherapy / targeting therapy, of which 22 (95.65%) were treated with first-line therapy and 1 (4.35%) were treated with second-line therapy. The median follow-up period was 6 months. 15 patients were assessed as remission (as of February 2022), of which 4 (17.39%) showed CR, 11 (47.83%) showed PR, 7 (30.43%) showed SD, and 1 (4.35%) showed PD. ORR was 65.22%, DCR was 95.65%. After 4 cycles of treatment, 14 patients (60.87%) achieved tumor remission and control, and the functional status score (KPS) increased from 65 to 85. The incidences of thyroid dysfunction, skin rash, fatigue, neutropenia and immune pneumonia were 2 (8.70%), 3 (13.04%), 2 (8.70%), 1 (4.35%) and 1(4.35%), respectively. Conclusions: This retrospective data have shown excellent efficacy and safety of pembrolizumab in the Chinese population of R/U/M head and neck squamous cell carcinoma, and provide data support for follow-up related research.Due to the short follow-up time, most of the patients have not yet reached PFS, and follow-up will continue.