Particle radiotherapy, or highly precise radiotherapy, has been applied to solitary hepatocellular carcinoma or hepatic oligometastases. However, radiotherapy for the multiple liver metastases is not feasible due to the low tolerant dose for whole liver irradiation. Although boron neutron capture therapy (BNCT) can deposit large dose gradient between tumors and surrounding normal tissues, it is difficult for BNCT to be applied to multiple liver metastases due to the poor distribution of thermal neutrons in the deep portion of the liver. In this chapter, we introduce two strategies to overcome this obstacle in applying BNCT to multiple liver metastases, which were executed by the Italian and Japanese BNCT groups. The Italian BNCT group treated multiple liver metastases from colon cancer with thermal neutron irradiation to the explanted liver (ex-vivo BNCT). The Japanese BNCT group treated multiple hepatocellular carcinomas with BNCT following administration of an emulsion of borocaptate sodium and liquid embolic agent via the hepatic artery. In addition, we present a case report on palliative BNCT for multiple liver metastases from thymic cancer with the same procedure as performed in BNCT for malignant brain tumors or head and neck cancers. BNCT has the potential to be applied to chemorefractory multiple liver metastases from the viewpoint of palliative use.