Cyclosporin A (Cyclosporin A) is a type of cyclic polypeptide antibiotic and is used as a medical drug. It is used to suppress the immune system of organ transplant patients, thereby reducing the risk of organ transplant rejection. However, due to the narrow effective therapeutic window and the potential for toxicity, it is necessary to monitor blood drug concentrations. In this study, cyclosporin A was added to human serum, extracted and purified using spin columns Monospin C18 and Ph, and analyzed by LC-MS/MS.