Objective To assess potential associations between sarcoma and gut microbiota using Mendelian randomization(MR)analysis.Methods Instrumental variables(IV)for gut microbiota were identified from summary data of a genome-wide association studies(GWAS)involving 18 340 participants from 24 cohorts published by the MiBioGen Consortium.The GWAS on sarcoma from Europe served as an outcome,involving 456 276 sarcoma patients.The inverse-variance weighted(IVW)method was used for primary analysis while sensitivity analysis was made to test the reliability of results of MR analysis.Results IVW results showed that Peptostreptococcaceae(OR=0.353,95％CI 0.127 to 0.979,P=0.045)and Faecalibacterium(OR=0.408,95％CI 0.173 to 0.961,P=0.040)had a negative causal correlation with sarcoma,but the Eubacterium fissicatena group(OR=2.216,95％CI 1.101 to 4.462,P=0.026)and Lachnospiraceae UCG008(OR=1.822,95％CI 1.005 to 3.305,P=0.048)exhibited a positive causal correlation with sarcoma.Sensitivity analysis showed no evidence of pleiotropy and heterogeneity.Conclusion Through two-sample MR,this study identifies a potential causal relationship between four gut microbiota and sarcoma.Peptostreptococcaceae and Faecalibacterium can reduce the risk of sarcoma while the Eubacterium fissicatena group and Lachnospiraceae UCG008 are linked to an increased risk of sarcoma.More research is required to find out more about the way gut microbiota influences the development of sarcoma.