Purpose: To explore the application value of ultrasound measurement of the cross-sectional area (CSA) of the iliac psoas muscle in diagnosing muscle mass loss in elderly (≥65 years old) type 2 diabetes mellitus (T2DM) patients. Methods: A total of 133 confirmed elderly T2DM patients from Zigong Fourth People's Hospital between November 2022 and May 2023 were selected as the observation group. According to the diagnostic criteria for MML, appendicular skeletal muscle mass (ASM) measured by bioelectrical impedance analysis and handgrip strength (HGS) measured by a handheld dynamometer were used as indicators. The study subjects were divided into MML group and non-MML group. Subsequently, the cross-sectional area of the iliopsoas muscle of the two groups of members was measured and recorded using ultrasound technology, and the average grayscale and sound intensity of the iliopsoas muscle were measured using DFY software.Key variables related to the presence of MML were identified using univariate analysis (t-test/chi-square test), followed by the construction of a multivariate logistic regression model (stepwise method) to reveal the independent risk factors for MML. The application value of meaningful indicators in diagnosing MML were assessed using sensitivity, specificity, accuracy, and area under the curve (AUC). Pearson correlation analysis was performed to evaluate the association between CSA and ASM, HGS. Results:There was no significant difference in age, average grayscale, and sound intensity of the iliopsoas muscle between the myopenia group and the non myopenia group (P > 0.05),but there were statistically significant differences in BMI and ultrasound CSA of the iliac psoas muscle between the two groups (P < 0.01). The MML group had lower BMI and ultrasound CSA of the iliac psoas muscle, with CSA values of 5.85 ± 1.73 cm2 for males and 7.51 ± 1.74 cm2 for females, and 4.51 ± 0.93 cm2 for males and 5.76 ± 1.30 cm2 for females. The logistic regression model showed that BMI (OR=0.852, P=0.036) and ultrasound area (OR=0.593, P=0.001) were protective factors for MML. CSA, BMI, and CSA+BMI were included in the regression model for diagnosing sarcopenia, respectively. The sensitivity, specificity, accuracy, and AUC of BMI sarcopenia were 53.8%, 74.2%, 72.2%, and 0.656, respectively; The sensitivity, specificity, accuracy, and AUC of CSA in diagnosing sarcopenia were 64.7%, 78.6%, 74.7%, and 0.723, respectively; The sensitivity, specificity, accuracy, and AUC of BMI combined with CSA in diagnosing sarcopenia were 62.4%, 81.2%, 75.9%, and 0.753, respectively. The combined model had an ideal effect.There was a significant correlation between CSA and ASM (r=0.53, P<0.01), as well as between CSA and HGS (r=0.55, P<0.01). The correlation between CSA and ASM was higher in females (r=0.50, P<0.01) than in males (r=0.30, P<0.05), while the correlation between CSA and HGS was higher in males (r=0.40, P<0.01) than in females (r=0.30, P<0.01). Conclusion: Ultrasound measurement of CSA of the iliac psoas muscle may be a highly valuable parameter in diagnosing MML in elderly T2DM patients, and it can help assess muscle mass and screen for MML.