Background: Poor social health is prevalent in older adults and may be associated with worse cognition, and increased dementia risk. The aim of this study was to determine whether social isolation, social support and loneliness are independently associated with cognitive function and incident dementia over 5 years in older adults, and to investigate potential gender differences. Methods: Participants were 11,498 community‐dwelling relatively healthy Australians aged 70–94,in the ASPREE Longitudinal Study of Older Persons(ALSOP).Social isolation, social support, loneliness and cognitive function were assessed through self‐report. Outcomes examined were cognitive decline(>1.5SD decline in cognitive performances in cebase line)and incident dementia(adjudicated according to DSM‐IV criteria).Results: Most participants self‐reported good social health(92%)with very few socially isolated(2%),with low social support(2%) or lonely(5%).Among women, social isolation and low social support were consistently associated with lower cognitive function(e.g., social support and cognitionβ =−1.17,p<0.001). No consistent longitudinal associations were observed between baseline social health and cognitive decline (over median 3.1 years) or incident dementia (over median 4.4years;social isolation: HR=1.00,p=0.99;low social support: HR=1.79,p=0.11;loneliness:HR=0.72,p=0.34 among women and men). Conclusion: Our study provides evidence that social isolation and a low social support are associated with worse cognitive function in women, but not men. Social health did not predict incident cognitive decline or dementia, but we lacked power to stratify dementia analyses by gender.