Hypertension or elevated blood pressure was documented to be an important risk factor for aortic diseases in observational studies, yet the causality remains to be determined. By applying a two-sample Mendelian randomization (MR) approach, we aim to determine whether hypertension or elevated blood pressure (systolic blood pressure [SBP] or diastolic blood pressure [DBP]) is linked causally to aortic aneurysm or aortic dissection. Genetic instruments and summary statistics for hypertension and aortic diseases were obtained from large genome-wide association studies. The traditional inverse variance weighted (IVW) method was used to obtain the causal estimates. Sensitivity analyses including MR-Egger, weighted median and multivariable MR were also performed. Our results suggested that genetic liability to hypertension was associated with aortic dissection (odds ratio [OR]: 1.81; 95% confidence interval [CI]: 1.27-2.58; P = 1.13 × 10-3) and aortic aneurysm (OR: 1.43; 95% CI: 1.22-1.66; P = 7.79 × 10-6). Per standard deviation increase in genetically-determined DBP was significantly associated with increased aortic dissection (OR: 1.14; 95% CI: 1.09-1.19; P = 1.58 × 10-9) and aortic aneurysm (OR: 1.07; 95% CI: 1.05-1.09; P = 8.37 × 10-14). There was a null association between SBP and aortic dissection (OR: 1.01; 95% CI: 0.99-1.94; P = 0.38) or aortic aneurysm (OR: 1.00; 95% CI: 0.99-1.01; P = 0.92). Sensitivity analyses documented similar results. Therefore, hypertension and elevated DBP are causally associated with higher risks of aortic aneurysm and aortic dissection. Preventive interventions for aortic diseases may consider individuals with hypertension, especially those with higher DBP. Meanwhile, further research is required to determine the mechanisms underlying the significantly greater correlation between DBP and aortic diseases than SBP.© 2023. The Author(s), under exclusive licence to The Japanese Society of Hypertension.