Objective To investigate the causal relationship between circadian rhythm disruption and inflammatory bowel disease(IBD)and the mediating effect of gut microbiota based on Mendelian randomization(MR).Methods Summary statistics of Genome-wide Association Study(GWAS)for circadian rhythm disruption(n=205 527)and IBD(n=214 053)were obtained from IEU OpenGWAS database.Summary statistics of GWAS for the gut microbiota were obtained from the MiBioGen database(n=18 340).Two-sample MR analysis was used to estimate the genetic correlation and causality between circadian rhythm disruption and IBD,and the mediating effect of the gut microbiota was analyzed by two-step MR analysis.Results There was a suggestive causal relationship between circadian rhythm disruption and IBD(odds ratio=1.255,P＜0.05).Rikenellaceae id.967 played a mediating role in the causal chain between them(the mediating effect was-0.028 740).Sensitivity analysis confirmed that the results were not interfered by level pleiotropy and heterogeneity.Conclusion There is a genetic correlation between circadian rhythm disruption and IBD,and gut microbiota may play a mediating role between them.