Objectives: The purpose of this study was to analyze the correlation between dietary selenium intake in fat-free mass index (FFMI) and handgrip strength among head-and-neck cancer patients undergoing chemoradiation therapy. Methods: A 2-week prospective cohort study was conducted at the Radiotherapy Unit of Dr. Cipto Mangunkusumo National General Hospital. Dietary selenium intake was estimated using the semi-quantitative food frequency questionnaire. FFMI was measured using bioelectrical impedance analysis (seca mBCA 525) and handgrip strength (HGS) using a Jamar dynamometer. Results: Fifty-three patients (median age 49 years) were included. Median dietary selenium intake was 81.3 μg/day. No significant correlation was observed between dietary selenium intake and changes in FFMI or HGS after adjustment for confounders. A weak correlation was found in the non-active hand (p=0.045), which should be interpreted with caution due to the short duration of observation and possible confounding. Conclusion: Within this short 2-week observation, dietary selenium intake was not significantly associated with changes in FFMI or HGS. The borderline finding in the non-active hand is likely an anomalous result and should be interpreted with caution. Longer-term studies with biomarker assessments are warranted. © 2025 The Authors.