BACKGROUND: Protein intake recommendations advise ≥0.8 g/kg body weight (BW)/d, whereas experts propose a higher intake for older adults (1.0-1.2 g/kg BW/d). It is unknown whether optimal protein intake differs by sex or race. OBJECTIVES: We examined the shape of sex- and race-specific associations of dietary protein intake with 3- and 6-y changes in appendicular lean mass (aLM) and gait speed and also 6-y incidence of mobility limitation in community-dwelling older men and women. METHODS: We used data on men (n = 1163) and women (n = 1237) aged 70-81 y of the Health, Aging, and Body Composition Study. Protein intake was assessed using an FFQ (1998-1999). aLM and gait speed were measured at baseline and at 3 and 6 y. Difficulty walking one-quarter mile or climbing stairs was measured every 6 mo over 6 y. Prospective associations were evaluated with linear and Cox regression models, comparing fit of models with and without spline functions. All analyses were stratified by sex and additionally by race. RESULTS: Mean ± SD protein intake was 0.94 ± 0.36 g/kg adjusted body weight (aBW)/d in men and 0.95 ± 0.36 g/kg aBW/d in women. There were no strong indications of nonlinear associations. In women, higher protein intake was associated with less aLM loss over 3 y (adjusted B per 0.1 g/kg aBW/d: 39.4; 95% CI: 11.6, 67.2), specifically in black women, but not over 6 y or with gait speed decline. In men, protein intake was not associated with changes in aLM and gait speed. Higher protein intake was associated with a lower risk of mobility limitation in men (adjusted HR per 1.0 g/kg aBW/d: 0.55; 95% CI: 0.34, 0.91) and women (adjusted HR: 0.56; 95% CI: 0.33, 0.94), specifically white women. CONCLUSIONS: Associations between protein intake and physical outcomes may vary by sex and race. Therefore, it is important to consider sex and race in future studies regarding protein needs in older adults.