Syk (spleen tyrosine kinase) is a non-receptor tyrosine kinase primarily expressed in immune cells such as B cells and T cells. It contains two SH2 domains and one catalytic kinase domain and participates in signal transduction following antigen recognition by interacting with members of the receptor immunoglobulin superfamily. Syk activates multiple signaling pathways, including calcium signaling pathways and the PI3K/Akt pathway, regulating cell activation, differentiation, and cytokine production. The activity and expression levels of Syk are crucial in inflammation and autoimmune diseases, and its genetic variations or functional dysregulation are associated with the development of certain immune system disorders. Due to its role in immune regulation, Syk has become an important target for drug development.