This cross-sectional study aimed to examine the accuracy of the Simplified Nutritional Appetite Questionnaire (SNAQ) and the SNAQ for Japanese Elderly (SNAQ-JE) for the Global Leadership Initiative on Malnutrition (GLIM)-defined malnutrition and sarcopenia screening in older persons. We included 380 inpatients aged ≥65 years (mean age, 79.3 ± 7.9; 60.0% women) and admitted to rehabilitation units. Undernutrition and sarcopenia were diagnosed based on GLIM criteria and the Asian Working Group for Sarcopenia, respectively, using bioimpedance analysis. Poor appetite was defined as an SNAQ score of <14 points and an SNAQ-JE score of ≤14 points. The sensitivity, specificity, and accuracy of these tools for detecting poor appetite for GLIM-defined malnutrition and sarcopenia were assessed. The rates of GLIM-defined malnutrition and sarcopenia were 56.8% and 59.2%, respectively. The number of patients with poor appetite was 94 (24.7%) for the SNAQ and 234 (61.6%) for the SNAQ-JE. The sensitivity and specificity of the SNAQ measured against GLIM-defined malnutrition were 32.9% and 73.1%, respectively, and against sarcopenia were 29.8% and 70.2%, respectively. The sensitivity and specificity of the SNAQ-JE measured against GLIM-defined malnutrition were 82.6% and 51.0%, respectively, and against sarcopenia were 86.0% and 53.7%, respectively. The SNAQ-JE showed fair accuracy for GLIM-defined malnutrition and sarcopenia in older patients admitted to rehabilitation units.