Background <p>Head and neck squamous cell carcinoma (HNSCC) is an aggressive epithelial malignancy with poor treatment outcomes. Although PIWI-interacting RNAs (piRNAs) have been recognized as important regulators of tumour biology, their roles in HNSCC remain largely unexplored.</p> Methods <p>Small RNA sequencing of paired tumour and adjacent normal tissues was performed to identify differentially expressed piRNAs. Functional assays in cell lines and xenograft models were used to evaluate the effects of piR-hsa-3636662 manipulation. RNA pull-down assays and immunoprecipitation were conducted to determine its interaction with the RNA-binding protein replication protein A1 (RPA1).</p> Results <p>piR-hsa-3636662 expression was markedly reduced in HNSCC tissues compared with their normal counterparts. The loss of this piRNA promoted cell proliferation, migration, and invasion, and accelerated tumour growth in vivo. Mechanistic studies showed that piR-hsa-3636662 binds directly to RPA1 and restrains its oncogenic function. Silencing RPA1 mitigated the malignant behaviors driven by piR-hsa-3636662 depletion.</p> Conclusions <p>This study identifies piR-hsa-3636662 as a previously uncharacterized tumour-suppressive piRNA in HNSCC. Our findings reveal that the piR-hsa-3636662–RPA1 pathway is a novel contributor to HNSCC progression and a candidate for therapeutic intervention.</p>