We examined the associations of maintaining or increasing physical activity (PA) for a 3-yr follow-up with subsequent incident inability to complete the 400-m walk test (i.e., mobility disability) for 6 yrs of follow-up in older adults. This study included 421 participants 65 yrs and older. The 400-m walk test was assessed at baseline and at 3-, 6-, and 9-yr follow-up. Physical activity was self-reported through a 6-point rating scale at baseline and 3-yr follow-up. Three-year cumulative PA (i.e., average at baseline and at 3-yr follow-up) and its changes (i.e., from baseline to 3-yr follow-up) were linked to subsequent incidence of mobility disability for 6 yrs of follow-up (i.e., from 3- to 9-yr follow-up), after adjustment for potential covariates. After the 3-yr period, incidence of mobility disability for the subsequent 6 yrs of follow-up occurred in 129 participants. The odds ratio (95% confidence interval) of incident mobility disability associated with 1-category increase in cumulative PA was 0.63 (0.41-0.97, P = 0.036). The odds ratio (95% confidence interval) of incident mobility disability associated with 1-category increase in changes in PA was 0.56 (0.38-0.84, P = 0.005). Hence, maintaining or increasing PA levels is associated with a reduced risk of mobility disability among older adults.