Soft tissue sarcoma is a very rare, malignant tumor that constitutes a family of more than 50 different subtypes with different prognostic outcomes. In most cases, neither chemotherapy nor conventional radiotherapy is an effective treatment option for these malignancies that can result in detrimental situations in unresectable cases. BNCT, however, may offer a viable method for the control of soft tissue sarcoma, even if only a few results of its applicability are available. A good antitumor effect of BNCT has been reported in the treatment of malignant peripheral nerve sheath tumor (MPNST). Moreover, clear cell sarcoma, a very rare, malignant tumor that responds to few treatments other than surgical resection, has demonstrated good outcome in not only basic studies but also clinical cases after BNCT application. This data suggests that BNCT is potentially effective in treating malignant soft tissue tumors. Further studies are warranted for developing BNCT as a treatment modality for soft tissue sarcoma.