Background &AimsMalnutrition and physical function impairment are prevalent concerns in long-term care facilities. This study investigated the relationship between quadriceps muscle thickness (QMT) or echo intensity (QEI), nutritional status, and activities of daily living (ADL) in residents of an Integrated Facility for Medical and Long-term Care (IFMLC) in Japan. MethodsUsing a cross-sectional design, 126 residents (86 women, median age 89 years) at an IFMLC were assessed. Malnutrition was diagnosed using the Global Leadership Initiative on Malnutrition (GLIM) criteria including disease burden/inflammation, while ADL status was evaluated using the Barthel Index (BI). QMT and QEI, indicative of muscle mass and intramuscular adipose tissue, were measured by ultrasound. Multivariate logistic and linear regression analyses were conducted to explore the association of QMT or QEI with malnutrition and ADL. Results62 residents (49%) were in the lower QMT group and 63 residents (50%) were in the upper QEI group. The prevalence of severe malnutrition in the lower QMT group was significantly higher than that in the upper QMT group. Moreover, the lower QMT group had significantly lower BI points than the upper QMT group. The upper QEI group had significantly lower BI points than the lower QEI group. lower QMT was associated with severe malnutrition (odds ratio 3.170; 95% CI 1.238 to 8.725; P = 0.016). Furthermore, both lower QMT (B = −12.520; 95% CI −17.069 to −7.973; P < 0.001) and upper QEI (B = −7.598; 95% CI −12.565 to −2.631; P = 0.003) showed an independent correlation with lower BI scores. ConclusionThis study found a relationship between lower QMT correlated with severe malnutrition and poor ADL, while higher QEI is associated with poor ADL.