Decreased mobility is a hallmark of aging. Olfactory dysfunction is common in older adults and may be associated with declines in mobility. To determine whether poor olfaction was associated with faster declines in mobility in older adults. This cohort study included 2500 participants from the Health, Aging, and Body Composition Study. Participants completed the Brief Smell Identification Test during the year 3 clinical visit (1999-2000) and were followed for up to 7 years. A data analysis was conducted between January and July 2023. Olfaction was defined as good (test score, 11-12), moderate (9-10), hyposmia (7-8), or anosmia (0-6). Mobility was measured using the 20-m usual and fast walking tests in clinical visit years 3 to 6, 8, and 10 and the 400-m fast walking test in years 4, 6, 8, and 10. The primary analyses included 2500 participants (1292 women 51.7%; 1208 men 48.3%; 960 Black 38.4% and 1540 White 61.6% individuals; mean SD age, 75.6 2.8 years). Multivariate-adjusted analyses showed that poor olfaction was associated with slower walking speed at baseline and a faster decline over time. Taking the 20-m usual walking test as an example, compared with participants with good olfaction, the speed at baseline was 0.027 (95% CI, 0-0.053) m/s slower for those with hyposmia and 0.034 (95% CI, 0.005-0.062) m/s slower for those with anosmia. Longitudinally, the annual decline was 0.004 (95% CI, 0.002-0.007) m/s/year faster for those with hyposmia and 0.01 (95% CI, 0.007-0.013) m/s/year faster for those with anosmia. Similar results were obtained for the 20-m and 400-m fast walking tests. Further, compared with participants with good olfaction, the odds of being unable to do the 400-m test were 2.02 (95% CI, 1.17-3.48) times higher for those with anosmia at the year 8 visit and 2.73 (95% CI, 1.40-5.35) times higher at year 10. Multiple sensitivity and subgroup analyses supported the robustness and generalizability of the findings. The results of this cohort study suggest that poor olfaction is associated with a faster decline in mobility in older adults. Future studies should investigate underlying mechanisms and potential health implications.