Abstract: Inosine 5'-monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme in de novo biosynthesis of guanine and plays an important role in cell proliferation. In clinic, IMPDH inhibitors are mainly used in fields of anticancer, antiviral, anti-parasitic, and immunosuppressive chemotherapy. However, since there are usually great inter-and intra-individual variability between drug concentration and clinical effect of IMPDH inhibitors, the enzyme activity of IMPDH may be applied as a specific biomarker and combined with the pharmacokinetics (PK) monitoring to improve efficacy and safety of IMPDH inhibitors. This review aims to discuss the assay of IMPDH activity measurement and its clinical application in recent years and provide valuable insights and theoretical basis for the development of IMPDH inhibitors' pharmacodynamics monitoring.