It is crucial to investigate age-related body composition changes in geriatric medicine. Bioelectrical impedance analysis (BIA) is easy to perform, non-invasive, relatively inexpensive, and portable. However, the accuracy of measurement by BIA is questionable. To develop and cross-validate the predictive equation for estimated appendicular skeletal muscle mass (ASM) using BIA in older community-dwelling Korean adults, we include two cohorts: study participants aged 65-80 years in the Ansung cohort for the Korean Health and Genome Study (men, n=285; women, n=435) used as equation-generating group, and Korean Longitudinal Study of Health Aging (KLoSHA) as cross-validation group (men, n=202; women, n=208). Dual energy X-ray absorptiometry (DXA) and BIA were performed in both cohorts. Using multiple linear regression analysis, we drew a predictive equation for DXA-measured ASM by BIA resistance. From DXA and BIA measurements in the Ansung cohort, we generated the estimated equation ASM (kg)=[(Ht(2)/R×0.104)+(age×-0.050)+(gender×2.954)+(weight×0.055)]+5.663 where Ht is height in centimeters; R is BIA resistance in 250Ω; for gender, men=1 and women=0; and age is in years. We validated this equation in the KLoSHA. The r(2) of the estimated ASM was 0.890. This BIA equation provides valid estimates of ASM in older Korean adults.