This study selected genome-wide association study data from the FinnGen database and utilized a bidirectional 2-sample Mendelian randomization (MR) method to explore the causal association between varicose veins (VV) and atrial fibrillation (AF). Inverse variance weighted (IVW) was used as the primary analytical method to assess the causal relationship between VV and AF, supplemented by Weighted median, MR-Egger and Simple 1mode. Cochran's Q test, MR-Egger regression intercept and Mendelian randomization pleiotropy residual sum and outlier were used as sensitivity analyses to detect heterogeneity and multilevel pleiotropy. Additionally, reverse MR was conducted to analyze the causal association between AF and VV. The IVW method indicated a positive causal relationship between VV and AF (odds ratio = 1.1571, 95% confidence interval = 1.0810-1.2384, P = 2.59 × 10-5). Reverse MR analysis shows no potential reverse causal relationships. The results showed a significant causal effect of VV on AF, suggesting that VV may increase the risk of developing AF. It also elaborates on the common risk factors and pathophysiological conditions between VV and AF.