Purpose <p>Head and neck cancers (HNC) significantly impact patients’ quality of life (QOL), with oral health often being significantly compromised, especially in advanced stages. Green tea, with its known anti-inflammatory and antioxidant properties, may help to improve oral health in these patients. Therefore, this study aims to investigate the effect of green tea–based mouth rinse on oral health status, pain, and QOL of advanced HNC patients.</p> Methods <p>This randomized controlled trial was conducted in the palliative care outpatient department of a tertiary hospital in New Delhi. Then, 64 patients with stage III/IV HNC receiving palliative care were randomly assigned to the experimental and control groups. In addition to usual care, the experimental group used a green tea–based mouth rinse thrice daily for 6&#xa0;weeks. The study examined oral health status as the primary outcome, which was assessed at baseline and every 2&#xa0;weeks up to 6&#xa0;weeks using the Oral Assessment Guide (OAG) and Oral Hygiene Index-Simplified (OHI-S). The secondary outcomes pain and quality of life of the patients were assessed using the Numerical Pain Rating Scale and Oral Health Impact Profile-14 (OHIP-14), respectively.</p> Results <p>Repeated measure ANOVA revealed that experimental group had significantly improved OAG-score (<i>F</i> = 34.32, <i>P</i> = &lt; 0.001, <i>ŋ</i>_<i>p</i>² = 0.39) and OHI-S-score (<i>F</i> = 5.67, <i>P</i> = &lt; 0.001, <i>ŋ</i>_<i>p</i>² = 0.11) over time. However, any significant between-group difference is not found in terms of pain (<i>P</i> = 0.73) and QOL (<i>P</i> = 0.34).</p> Conclusion <p>Green tea–based mouth rinse was found to be effective in improving the oral health status of advanced HNC patients. Nurses should incorporate such cost-effective options to improve the oral health of cancer patients.</p> Trial Registration Details <p>The trial had been registered under the Clinical Trial Registry of India on 17/05/2024. (Registration No: CTRI/2024/05/067571).</p>