Background <p>Liver cancer has high rates of both incidence and mortality. Conventional imaging modalities (US, CT and MRI) and ¹⁸F-fludeoxyglucose (FDG) PET/CT demonstrate limited efficacy in accurately detecting primary and metastatic hepatic lesions. Due to the high expression of fibroblast activation protein (FAP) on cancer-associated fibroblasts (CAFs) in the tumor stroma, FAP inhibitor (FAPI) PET imaging has become a promising tool in the diagnosis and staging of liver cancer.</p> Methods <p>Using the search terms (FAPI) AND ((Liver) OR (Hepatic)), 216 papers were found in the PUBMED database for the period January 2018 through January 2025. Among these articles, 51 studies related to “suspected liver cancer” or “detection of liver metastases” were included. We summarized the state of the art in FAPI PET imaging in primary and metastatic liver cancer, compares the diagnostic efficiency with FDG. In addition, we analyzed common reasons for the appearance of false-positive uptake.</p> Results <p>The primary focus of this review is to compare the diagnostic capabilities of FAPI and FDG in primary and metastatic liver cancer. FAPI PET showed higher detection efficacy than ¹⁸F-FDG in primary and metastatic liver cancer and had potential in detecting different pathological grades of hepatocellular carcinoma (HCC) lesions and small lesions. FAPI PET also has the potential to be used for restaging liver cancer and adjustment of therapeutic protocol. However, inflammatory, liver fibrosis and some benign tumors may lead to false-positive FAPI results in the diagnosis of HCC. In addition, we briefly discuss the biological mechanisms of FAP expression in tumors and how these mechanisms affect FAPI PET/CT uptake.</p> Conclusion <p>This review provides the state of the art in FAPI PET imaging in primary and metastatic liver cancer, compares the diagnostic efficiency with FDG, and discusses the results of FAPI false positives and underdiagnosis.</p>