Objective To explore the causal relationship between Omega-3 fatty acids and the risk of breast cancer via Mendelian randomization analysis.Methods Analysis was conducted on data from genome-wide association studies(GWASs)on Omega-3 fatty acids and breast cancer.The selected instrumental variables(IVs)comprised genetic loci associated with Omega-3 fatty acids.Various Mendelian randomization analysis methods,including inverse-variance weighted(IVW)method,MR-Egger regression analysis,weighted median,simple models,and weighted models,were used to evaluate the causal relationship between Omega-3 fatty acids and the risk of breast cancer.Results A total of 47 single-nucleotide polymorphisms strongly associated with Omega-3 fatty acids were selected as IVs.The analysis methods,including IVW method,revealed no causal relationship between Omega-3 fatty acids and the risk of breast cancer(P>0.05).Analysis methods,such as MR-Egger regression analysis,did not detect significant gene-level pleiotropy(P=0.319),which indicates the high sensitivity and robustness of analysis results.Conclusion The findings of this study suggest the absence of a causal relationship between Omega-3 fatty acids and the risk of breast cancer.