Abstract: Currently, extracellular concentration measurement is the major approach of therapeutic drug monitoring (TDM) of clinical immunosuppressant in organ transplantation. Its correlation with the efficacy of immunosuppressant remains elusive. With widespread application of liquid chromatography, the detection technology of intracellular concentration of immunosuppressant is gradually mature. Theoretically, it may more accurately reflect the efficacy of immunosuppressant due to that the level of drug exposure in target cells can be directly measured. In this article, the history and present situation of the determination of intracellular concentration of immunosuppressant were summarized, and the association between the determination methods of intracellular concentration of immunosuppressant and drug efficacy was emphatically analyzed. Detection of intracellular concentration of immunosuppressant possesses better application value in clinical practice, which is worthy of promotion in clinical settings.