Objective <p>Myopia is a common eye disease, and the effect of allergic diseases on myopia is unclear. This study was to explore the causal relationship between allergic diseases and myopia risk through a two-sample Mendelian randomization (MR) analysis.</p> Materials and Methods <p>Genetic variants related to allergic diseases (allergic conjunctivitis, atopic dermatitis, allergic rhinitis, and asthma) and immunoglobulin E and myopia were extracted from the MRC-IEU Open genome-wide association studies (GWAS) project. The results of MR were based on the inverse-variance weighted (IVW) analysis. The odds ratio (OR) and 95% confidence interval (CI) were used to report causal relationships.</p> Results <p>Genetically predicted asthma [IVW: OR = 1.233 (95% CI: 1.043-1.456), <i>P</i> = 0.0140] and higher immunoglobulin E levels [IVW: OR = 1.136 (95% CI: 1.020–1.265), <i>P</i> = 0.0207] increased the risk of myopia. There was no significant causal relationship between allergic conjunctivitis (IVW: <i>P</i> = 0.2916), atopic dermatitis (IVW: <i>P</i> = 0.3168), and allergic rhinitis (IVW: <i>P</i> = 0.8297) and risk of myopia. Further analysis revealed that the causal correlation of immunoglobulin E levels with myopia risk was caused by outliers.</p> Conclusions <p>Genetically predicted asthma increased the risk of myopia.</p>