Background/Objectives: Quantitative And Qualitative Decline Of Thigh Muscle May Play An Essential Role In The Development Of Immobility And Frailty In Elderly. We Aimed To Validate The Correlation Between Estimated Dominant Thigh Muscle Volume And Physical Performance Of Lower Limbs In Older Adults. Additionally, The Association Between Dominant Thigh Muscle Index And Frailty Was Studied. Measurements: One Hundred Eighty-Nine Elderly Adults, Aged 65-90, Were Recruited At Ambulatory Clinics. The Anthropometric Measurements, Appendicular Skeletal Muscle Mass (ASM) Using Bioelectrical Impendence Analysis, Quadriceps Muscle Strength, Physical Performance Including Timed Up&Go Test, 5m Walking Speed, And Grip Strength Were Examined At Baseline And 1 Year Thereafter. The Fried Frailty Index Was Evaluated Concurrently And Pre-Frail Along With Frail Status Were Combined For Analysis. Results: 148 Out Of 189 Subjects Completed The Study. Estimated Dominant Thigh Muscle Volume Using Anthropometric Measurements Was Positively Correlated To Quadriceps Muscle Strength And ASM, Whereas It Was Negatively Correlated With Timed Up&Go And 5m Walking Speed Significantly. Dominant Thigh Muscle Index (Quadriceps Muscle Strength Per Thigh Muscle Volume*1000) Was Marginally Different at National Health Research Institute on June 3, 2012Between Gender (P=0.06). Additionally, Being Older, Having Weaker Quadriceps Muscle Strength, Thigh Muscle Index, And Longer Timed Up&Go Test Were Associated With Frail Status (All P-Value < 0.05). Dominant Thigh Muscle Index Was An Independent And Protective Factor Associated With Frailty After Age Adjusted. Conclusions: Using The Equation With Anthropometric Measurements Is A Simple And Noninvasive Method For Thigh Muscle Volume Estimation. Thigh Muscle Index Can Early Detect Frailty Stage And Minimize Gender Difference.