Abstract: Cancer-associated fibroblasts (CAFs) are the essential components in the tumor microenvironment. Fibroblast activation protein (FAP) is a promising theranostic target because it is highly expressed in the CAFs of tumor stroma but lowly expressed in most of the normal tissue. Recently, a burst of studies reported the research progress of radiolabeled FAP-targeted molecular probe for tumor diagnosis as well as radionuclide therapy. For comprehensively understanding the clinical value of FAPI probe in tumoral nuclear medicine, this review summarizes the state-of-the-art of FAP inhibitors-based molecular imaging probe (FAPI) for cancer diagnosis, clinical therapeutic regimen improvement, and targeted radionuclide therapy.