Background: Sarcopenia (low muscle mass) and myosteatosis (fat infiltration of muscle) can be assessed from routinely obtained Computed tomography (CT) images and are independent predictors of chemotherapy toxicities and survival among patients with gastrointestinal (GI) malignancies. However, most studies to date have consisted of predominantly white populations. Therefore, the role of sarcopenia and myosteatosis among racial minority populations is unknown. Our objective was to examine racial differences in muscle measures and their association with survival among older adults with GI malignancies. Methods: This is a prospective cohort study of older adults with GI cancers from the University of Alabama at Birmingham. Single slices of axial CT images from L3 segments were analyzed using Slice-O-Matic software. Skeletal muscle area (cm²) was divided by height to obtain the skeletal muscle index (SMI, cm²/m²). Skeletal muscle radiodensity (SMD) in Hounsfield units (HU) was used to approximate muscle composition. Sarcopenia (low SMI) and myosteatosis (low SMD) were defined based on standard cut-offs developed in a cohort of GI malignancies (Martin et al., JCO 2013). We compared differences in muscle measures between non-Hispanic (NH) White and NH Black participants. We utilized Cox models, separated by race, to examine the impact of muscle measures on survival. We adjusted for age, sex, education, cancer type, cancer stage, lines of therapy, and comorbidities. Results: Six hundred sixty patients were included, 76% NH White and 24% NH Black. The median age was 69.4 years, 35% had colorectal cancer, and 42% had stage IV disease. NH Black patients had higher SMD (41.7 vs. 38.3 HU; p < 0.001) and lower rates of myosteatosis (40% vs. 27%; p = 0.04) but similar SMI (42.3 vs. 41.1 cm²/m²) and rates of sarcopenia (58% vs. 55%). In stratified Cox models, each 5 HU unit increase in SMD was associated with reduced risk of all-cause mortality of NH black patients (HR 0.88; 95% CI 0.80-0.98 p = 0.02) and not in NH White patients (HR 0.95; 95% CI-0.88-1.01; p = 0.14). Meanwhile, each 5-unit increase in SMI was associated with improved survival in NH White patients (HR 0.91; CI 0.85-0.98; p = 0.03) but not in NH Black patients (HR 0.89 CI0.78-1.03 p = 0.13). When using existing cut points for sarcopenia and myosteatosis, NH White patients with sarcopenia had worse survival (HR 1.42; CI 1.04-1.92; p = 0.02), but sarcopenia among NH black patients was not associated with worse survival (HR 1.16 95% CI 0.62-2.16 p = 0.64). Myosteatosis was not associated with worse survival in either NH white (HR 95%CI 0.95-1.68 p = 0.10) or NH black patients (HR 1.61 95%CI 0.88-2.95 p = 0.12). Conclusions: Muscle measures may differ by race and have different associations with survival by racial group. Therefore, it is essential to develop cut points for muscle measures incorporating race.