: Hyperuricemia is an established risk factor for cardiovascular disease, including atrial fibrillation (AF). The prevalence of hyperuricemia and its clinical significance in patients with already diagnosed AF remain unexplored. : The Polish Atrial Fibrillation (POL-AF) registry includes consecutive patients with AF hospitalized in 10 Polish cardiology centers from January to December 2019. This analysis included patients in whom serum uric acid (SUA) was measured. : From 3999 POL-AF patients, 1613 were included in the analysis. The mean age of the subjects was 72 ± 11.6 years, and the mean SUA was 6.88 ± 1.93 mg/dL. Hyperuricemia was found in 43% of respondents. Eighty-four percent of the respondents were assigned to the high cardiovascular risk group, and 45% of these had SUA >7 mg/dL. Comparison of the extreme SUA groups (7 mg/dL) showed significant differences in renal parameters, total cholesterol concentration, and left ventricular ejection fraction (EF). Multivariate regression analysis showed that SUA >7 mg/dL (OR 1.74, 95% CI 1.32-2.30) and GFR <60 mL/min/1.73 m (OR 1.94, 95% CI 1.46-2.48) are significant markers of EF <40% in the study population. Female sex was a protective factor (OR 0.74, 95% CI 0.56-0.97). The cut-off point for SUA with 60% sensitivity and specificity indicative of an EF <40% was 6.9 mg/dL. : Although rarely assessed, hyperuricemia appears to be common in patients with AF. High SUA levels may be a significant biomarker of reduced left ventricular EF in AF patients.