To explore the relationship of general health decline assessed by frailty and risk of dementia and Alzheimer's disease (AD). A seven-year prospective cohort study. Secondary analysis of data from the Beijing Longitudinal Study on Aging. Urban and rural communitydwelling people aged 60 and older at baseline. Frailty was quantified using the deficit accumulation-based frailty index (FI), constructed from 40 health deficits at baseline. Dementia was diagnosed by DSM-IIIR. AD and vascular dementia (VaD) were diagnosed by NINCDS-ADRDA and NINDS-AIREN. The relationships between frailty and the risk of dementia, AD and death were evaluated through multivariable models. Of 2788 participants at baseline (1997), 171 (11.1%) reported a history of dementia. In seven years, 351 people developed dementia (13%: 223 AD and 128 other types of dementia) and 813 died (29%). After adjustment for age, sex, education, and baseline cognition, baseline frailty status significantly associated with Alzheimer's disease and dementia and death. For each deficit accumulated, the odds ratio of death increased by 5.7%, and the odds ratio of dementia increased by 2.9% (p < 0.001). Frailty was associated with Alzheimer's disease and dementia over a seven years period. Frailty index might facilitate the identification of older adults at high risk of dementia for the application of the most effective, targeted prevention strategies.