Objective: Malnutrition is a common health concern among the older population. In Taiwan, older adults are required to score 90 or higher on the Barthel Index (BI) to qualify for admission to public long-term care institutions; however, they are not ob-ligated to undergo nutritional assessments. This study demonstrated the utility of the BI in determining nutritional status when older adults are referred to public long-term institutions. Methods: In this multicentre cross-sectional study, 251 residents aged 70 years or older at three nursing homes in Taiwan were evaluated between November 2010 and May 2011. Information on participants’ health history was collected, in-cluding BI scores, Mini Nutritional Assessment results, and previous responses to a questionnaire on dental health and swallowing capacity. Results: The mean age and BI score were 82.9 (SD 5.6) and 88.8 (SD 21.7), respectively. Among the study sample, 123 (49.0%) participants were identified as having a risk of malnutrition. The BI had high accuracy (area under the receiver operating characteristic curve, 79.1%) when used to predict the risk of malnutrition. Lower BI scores were associated with a higher risk of malnutrition. Of all BI items, the stair-climbing item had the highest correlation with nutritional status (Cohen’s standardised effect size [ES]: 0.90), followed by mobility and chair–bed transfers (both ESs: 0.76). Conclusion: We emphasise that preventing worsening malnutrition in older long-term care residents is crucial. The present study revealed that the BI can help with the primary assessment of nutritional status in older adult men, although it cannot be a decisive tool by itself for nutritional status assessment.