BACKGROUND: The aging process is related to cerebrovascular dysfunction and physiological changes, such as reduced pulmonary function. This ultimately induces cognitive impairment or dementia. OBJECTIVE: This study aimed to determine the relationship between aging-related pulmonary function, cognition, motor function, and activities of daily living (ADLs) in older adults with dementia. METHODS: This cross-sectional study included 69 older adults diagnosed with dementia. Aging-related pulmonary function and cognition were measured using a hand-held spirometer and the Korean version of the Mini-Mental State Examination (MMSE-K), respectively. To assess motor function and ADLs, the Berg Balance Scale (BBS), 10-meter walk test (10-MWT), 6-minute walk test (6-MWT), and modified Barthel index (MBI) were used to measure balance, walking speed, physical functional capacity (or walking tolerance), and ADLs, respectively. All data were analyzed using the Pearson’s product correlation coefficient (r). RESULTS: Forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) as measures of aging-related pulmonary function correlated only with the 6-MWT (FVC: r = 0.483, p = 0.002; FEV1: r = 0.512, p = 0.001). In cognitive function, MMSE-K was associated with BBS (r = 0.283, p = 0.022) and MBI (r = 0.454, p = 0.000). Additionally, there were significant correlations (r = 0.425–0.671, p = 0.000) between all motor function and ADLs measures in older adults with dementia. CONCLUSIONS: Our findings demonstrated that aging-pulmonary function was related to a lower physical functional capacity, and hence, suggested that the reduced pulmonary function were unable to walk for longer distance in older adults with dementia.