Previous studies have suggested a comorbidity between autoimmune thyroid disease (AITD) and urticaria. However, the causal effects between AITD and urticaria remain unclear. This study employed genome-wide association study (GWAS) data to analyze the associations between AITD and urticaria through bidirectional Mendelian randomization (MR), meanwhile, examined the role of 731 immune traits as mediators between the two diseases through mediation analysis. The IVW results indicated that Graves' disease (GD) and Hashimoto's thyroiditis (HT) have a potential risk effect on urticaria, particularly increasing the risk of other and unspecified urticaria and idiopathic urticaria. Urticaria, mainly other and unspecified urticaria, dermatographic urticaria demonstrated a potential risk effect on HT. The mediation analysis revealed that GD likely increases the risk of other and unspecified urticaria by reducing CD4