Objectives: Patients with chronic kidney disease (CKD) are known to develop sarcopenia, an agingrelated disorder, with low muscle mass, strength and physical performance. Ultrasound-derived thigh muscle and rectus femoris thickness (TMT and RFT) can be measured easily in clinical practice, but need validation for use in predialysis CKD (stages III through V) for muscle mass estimation. The study aims to compare ultrasound-derived TMT and RFT with bioelectrical impedance analysis (BIA)-derived muscle mass estimation in the diagnosis of sarcopenia in predialysis CKD. Methods: Patients with stable CKD stage III, IV, V and not yet on dialysis were recruited, and underwent anthropometric assessment, BIA and ultrasound examination of midthigh region. Appendicular skeletal muscle index (ASMI)/height2 derived from BIA was taken as a standard for the diagnosis of low muscle mass. Gait speed and handgrip were also measured. The Asian Working Group criteria were applied. Cutoff values for low muscle mass by TMT and RFT were obtained using receiver operator curve (ROC) analysis. Results: Of the total of 117 enrolled study participants, 52 (45%) had low muscle mass, 34 (29%) had sarcopenia, of whom 79% were male, majority (38%) were CKD stage IV and had a mean age of 58 years. Using ROC analysis, TMT cutoffs of 19 mm in males and 17 mm in females were computed. Comparison of TMT cutoffs and ASMI/h2 showed good agreement between the 2 methods using Bland-Altman plots. Conclusions Ultrasound-derived TMT and RFT can be used for muscle mass estimation in the diagnosis of sarcopenia.