Abstract: Diabetes is a major health problem and has become a burden to the health care system worldwide. Malnutrition is common among patients with diabetes, both in hospitalized and outpatient clinic settings. Therefore, nutrition screening is needed to detect malnutrition risk. Recently, a new nutrition-screening tool for adult populations has been developed, termed the Simple Nutrition Screening Tool (SNST). SNST has been validated for use in adult hospitalized patients. This study aimed to determine the validity (sensitivity, specificity, Maximum Sum Sensitivity and Specificity [MSSS] and Area Under Curve [AUC]) of SNST and SGA in calculating the body mass index in type 2 diabetic patients. This observational study employed a cross sectional design. A total of 153 type 2 diabetic outpatients from an internal medicine clinic at Dr Moewardi Hospital were recruited using a purposive sampling technique. The independent variables included nutrition-screening interpretation using SNST and SGA, while the dependent variable was body mass index (BMI). Contingency tables and the ROC curve were used to determine the validity of SNST and SGA compared with standards for nutrition and body mass index. There ware significant associations between SNST and BMI (p<0.001) and SGA and BMI (p<0.001). Validation of SNST vs. SGA revealed the following: sensitivity, 88.89% vs. 77.78%; specificity, 81.25% vs. 81.94%; MSSS, 170.14% vs. 159.72% and AUC, 0.851 vs. 0.799. SNST exhibited better validity than SGA predicting the body mass index of type 2 diabetic patients.