Omega-3 fatty acids may be protective against bipolar disorder (BD), whereas omega-6 fatty acids and an increased omega-6:omega-3 ratio may increase the risk of BD. This causal relationship has not yet been established. We attempted to prove the existence of these causal relationships in this study. Datasets on omega-3, omega-6, and omega-6:omega-3 ratios were obtained from the UK Biobank. The EBI database was used to obtain the BD dataset. SNPs associated with fatty acids were identified as instrumental variables (IVs) that met the criteria of P < 5 × 10-8, LD (R2 > 0.01), and kb < 10 000. The main analytical method in this study was the inverse variance weighted (IVW) method. Furthermore, we employ a variety of methods for sensitivity analysis. According to the IVW analysis, higher omega-3 levels were associated with a lower risk of BD (OR = 0.884, 95%CI: 0.796-0.982, P < 0.05). An increase in the omega-6:omega-3 ratio was associated with an increased risk of BD (OR = 1.172, 95%CI: 1.046-1.314, P < 0.05), but no causal relationship between omega-6 levels and BD risk was unearthed. Our MR findings suggest that the ratio of omega-3, omega-6:omega-3 is associated with the risk of BD. It is important to be concerned about the risk of BD in individuals with low serum omega-3 intake and a high omega-6:omega-3 ratio.