Objective To analyze the correlation between Non-Alcoholic Fatty Liver Disease(NAFLD)and Ulcerative Colitis(UC)by two-way Mendelian Randomization analysis(MR),to clarify the causal effect of the two.Methods A genome-wide association study(GWAS)statistical database was selected for the two-way MR analysis of the two samples.Results Inverse-Variance Weighted(IVW),weighted median,weighted multinomial,MR-Egger regression and MR-PRESSON were used.Results NAFLD possessed a causal effect on UC(OR=1.06,95%CI:1.01~1.11,P=0.01),reverse causality analyses did not find a significant causal effect of UC on NAFLD.The results of sensitivity analyses suggested that horizontal pleiotropy would have no effect on the causal estimates.Conclusion A causal relationship exists between NAFLD and UC,including the results of the reverse causality analysis.