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Objective To explore the bidirectional causal relationships between periodontitis and asthma using the two-sample Mendelian randomization (MR) method to provide a basis for exploring the etiology and formulating preventive and therapeutic measures of periodontitis and asthma. Methods We performed two-sample bidirectional Mendelian randomization analysis using publicly released European genome-wide association studies (GWAS) statistics for periodontitis (<i>n</i> = 34 615) and asthma (<i>n</i> = 408 422). The inverse variance weighted (IVW) method was employed as the main approach to estimate the bidirectional causal relationships between periodontitis and asthma. In addition, weighted median (WM), MR-Egger regression, maximum likelihood, and Mendelian randomization robust adjusted profile score (MR-RAPS) were used as supplementary analyses. Sensitivity analyses were conducted using Cochran's <i>Q</i> test, Mendelian randomization pleiotropy residual sum and outlier (MR-PRESSO), and leave-one-out analysis. Results A total of 12 and 43 single-nucleotide polymorphisms (SNPs) were included as instrumental variables for periodontitis and asthma, respectively. The results of IVW, WM, MR-Egger regression, maximum likelihood, and MR-RAPS showed that periodontitis was not causally related to the risk of asthma (IVW: <i>OR</i>: 1.003, 95% <i>CI</i>: 0.973-1.035, <i>P</i> = 0.828, WM: <i>OR</i>: 0.990, 95% <i>CI</i>: 0.951-1.031, <i>P</i> = 0.641; MR-Egger regression: <i>OR</i>: 0.988, 95% <i>CI</i>: 0.960-1.028, <i>P</i> = 0.573; maximum likelihood: <i>OR</i>: 1.003, 95% <i>CI</i>: 0.972-1.035, <i>P</i> = 0.834; MR-RAPS: <i>OR</i>: 1.002, 95% <i>CI</i>: 0.970-1.036, <i>P</i> = 0.890) among the European population, and no causal effect of asthma on periodontitis was found (IVW: <i>OR</i>: 1.021, 95% <i>CI</i>: 0.938-1.111, <i>P</i> = 0.633, WM: <i>OR</i>: 1.011, 95% <i>CI</i>: 0.894-1.142, <i>P</i> = 0.866; MR-Egger regression: <i>OR</i>: 1.042, 95% <i>CI</i>: 0.824-1.319, <i>P</i> = 0.731; maximum likelihood: <i>OR</i>: 1.021, 95% <i>CI</i>: 0.938-1.112, <i>P</i> = 0.631; MR-RAPS: <i>OR</i>: 1.017, 95% <i>CI</i>: 0.931-1.110, <i>P</i> = 0.713) among the European population. Cochran's <i>Q</i> test showed no heterogeneity among the included instrumental variables, MR-PRESSO test found no horizontal pleiotropy, and the leave-one-out method did not identify outlier SNPs. Conclusion The results of this study, based on European genetic data, do not support a bidirectional causal association between periodontitis and asthma in the European population.