Objective:To investigate the frailty status in elderly patients with atrial fibrillation(AF)and the underlying factors.Methods:In this prospective study, a total of 400 elderly hospitalized patients with AF from May 2017 to October 2021 were consecutively enrolled, 65.8% of whom were men(263), with an average age of 83(75, 90)years.According to age, 90 patients were between 65 and 74 years old, 137 were between 75 and 84 years old, and 173 were ≥85 years old.AF patients' frailty was assessed by the FRAIL scale, and logistic regression was employed to analyze related factors.Results:The overall prevalence of frailty was 41.25%(165)in the elderly AF patients, with 10.00%(9)in the 65-74 year-old group, 33.58%(46)in the 75-84 year-old group, and 63.58%(110)in the ≥85 year-old group.Clinical features of frail elderly patients with AF included a lower body mass index, longer hospitalization days, a faster heart rate on admission, a higher age-adjusted Charlson comorbidity index(ACCI), a higher non-valvular atrial fibrillation stroke risk score(CHA 2DS 2-VASc), a higher bleeding risk score(HAS-BLED), use of fewer anticoagulant drugs, and higher proportions with old myocardial infarction, congestive heart failure and anemia.Comprehensive geriatric assessment revealed that this population usually had a lower score for activities of daily living(ADL), a lower mini nutritional assessment-short form(MNA-SF)score, a lower Mini-Cog test score, and a higher fall risk score.These patients also exhibited higher high-sensitivity C-reactive protein, lower hemoglobin, lower albumin, a lower glomerular filtration rate(eGFR), lower total cholesterol, and lower apolipoprotein B, all with statistical significance( P<0.05). Logistic regression analysis showed that age( OR=1.068, 95% CI: 1.027-1.111, P<0.01), high-sensitivity C-reactive protein( OR=1.049, 95% CI: 1.024-1.075, P<0.01), and CHA 2DS 2-VASc score( OR=1.328, 95% CI: 1.083-1.628, P<0.01)increased, and albumin( OR=0.854, 95% CI: 0.786-0.929, P<0.01), MNA-SF score( OR=0.830, 95% CI: 0.747-0.923, P<0.01), and Mini-Cog score( OR=0.845, 95% CI: 0.717-0.997, P<0.05)decreased, and these were factors associated with the prevalence of frailty in elderly AF patients. Conclusions:The prevalence of frailty in elderly patients with AF is high.Elderly patients with AF are more likely to develop frailty with advanced age, poor nutrition and cognitive status, a high risk of stroke and high levels of inflammatory factors.