Abstract: Para-neoplastic neurological syndrome (PNS) is a series of rare illnesses affecting the nervous system and associated with several malignant tumors. PNS is manifested by various clinical symptoms, which conventionally precede the diagnosis of tumors in months or even years. Although anti-neuronal antibodies can indicate the presence of cancer, numerous false positive and false nega-tive cases are detected. Therefore, the clinical diagnosis of PNS has become a challenge. Position emission tomography/computed to-mography (PET/CT) is an image-fusion method containing anatomical and functional information and can be used to obtain whole-body images by a single scan. Fluoro-deoxy-glucose (FDG) PET/CT imaging can reveal potential malignant lesions in the whole body and diagnose specific types of cancer. This technology can also be applied to assess functional abnormality in the brain and moni-tor its response to treatment. Furthermore, the mechanism, clinical manifestation, and diagnosis of PNS are introduced in this study. Re-cent applications of FDG PET/CT in the diagnosis of PNS are reviewed to improve diagnostic accuracy.