Purpose Concurrent chemoradiotherapy (CCRT) is one of the standard treatments for patients with advanced head and neck squamous cell carcinoma (HNSCC). However, CCRT may lead to decreased quality of life (QoL) and treatment compliance. This study aimed to determine the effects of PG2 (Astragalus polysaccharides) injection on CCRT-associated adverse events (AEs) and patients’ compliance with the CCRT course. Methods In this phase II double-blind randomized placebo-controlled trial, PG2 injection (sterile powder form) or placebo was administrated three times per week in parallel with CCRT to patients with HNSCC. The chemotherapy regimen included 50 mg/m 2 cisplatin every 2 weeks with daily tegafur–uracil (300 mg/m 2 ) and leucovorin (60 mg/day). Results The study was terminated prematurely due to the successful launch of a newly formulated PG2 injection (lyophilized form). A total of 17 patients were enrolled. The baseline demographics and therapeutic compliance were comparable between the CCRT/PG2 and CCRT/placebo groups. During CCRT, severe treatment-associated AEs were less frequent in the CCRT/PG2 group than in the CCRT/placebo group. Furthermore, less QoL fluctuations from the baseline during CCRT were noted in the CCRT/PG2 group than in the CCRT/placebo group, with a significant difference in the pain, appetite loss, and social eating behavior. The tumor response, disease-specific survival and overall survival did not differ between the two groups. Conclusion This preliminary study demonstrated PG2 injection exhibited an excellent safety profile, and has potential in ameliorating the deterioration in QoL and the AEs associated with active anticancer treatment among patients with advanced pharyngeal or laryngeal HNSCC under CCRT. Further research in patients with other cancer types or treatment modalities may widen PG2’s application in clinical settings.