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BACKGROUND It remains unclear whether oral anticoagulation (OAC) can prevent dementia or cognitive impairment (CI) in patients with atrial fibrillation (AF). OBJECTIVE To investigate the risk of dementia/CI among AF patients with and without OAC treatment. METHODS We conducted a retrospective cohort study using UK primary care data (2000-2017). Participants with newly diagnosed AF without a history of dementia/CI were identified. Inverse probability of treatment weights based on propensity-scores and Cox regression were used to compare the dementia outcomes. RESULTS Among 84,521 patients with AF, 35,245 patients were on OAC treatment, 49,276 received no OAC treatment and of these, 29,282 patients were on antiplatelets. Over a mean follow-up of 5.9 years, 5,295 patients developed dementia/CI. OAC treatment was associated with a lower risk of dementia/CI compared to no OAC treatment (hazard ratio (HR) 0.90, 95% confidence interval (CI), 0.85-0.95, p<0.001) or antiplatelets (HR=0.84, 95% CI=0.79-0.90, p<0.001). No significant difference in dementia risk was observed for direct oral anticoagulants (DOACs) versus warfarin (HR 0.89, 95% CI, 0.70-1.14, p=0.373), whereas dual therapy (OAC plus an antiplatelet agent) was associated with a higher risk of dementia/CI compared with no treatment (HR 1.17, 95% CI, 1.05-1.31), p=0.006). CONCLUSION OAC use was associated with a lower risk of dementia/CI compared to non-OAC and antiplatelet treatment among AF patients. The evidence for DOAC on cognitive function is insufficient and further studies including randomized clinical trials are warranted.