Objective:To investigate whether there was a potential two-way causal relationship between sleep disorder(SD)and the incidence of gastric ulcer(GU)by two sample Mendelian randomization(MR)analysis.Methods:The data sets of exposure and outcome were obtained from IEU database,from which suitable Single Nucleotide Poly Morphisms(SNPs)were selected as instrumental variables(IVs),and then inverse variance weighting(IVW),MR-Egger regression,weighted median(WME),simple model and weigh-ted model were used for two-way MR Analysis.Cochran's Q test and MR-Egger intercept test were used for sensitivity analysis.Results:The IVW method showed that there was a significant unidirectional causal relationship between SD and the incidence of GU.When SD were used as exposure factors,the positive MR Analysis had significant statistical significance(OR=1.009,95%CI:1.004～1.015,P=0.001).When GU used as an exposure factor,reverse MR Analysis was not statistically s-ignificant(OR=1.197,95%CI:0.425～3.371,P=0.734).Further sensitivity analysis showed no significant heterogeneity and horizontal pleiotropy.Conclusion:Mendelian randomization analysis found that there is a potential one-way causal relationship between SD and the risk of GU,and SD are risk factors for GU.