Carborane shows high levels of hydrophobicity, thermal stability, and chemical stability. The hydrophobicity of carborane has been used to form interactions with the hydrophobic core of bioactive proteins. We have designed and synthesized carborane-bearing pullulan using carborane as a hydrophobic core to prepare physically crosslinked nanogels. The resulting amphiphilic polysaccharide formed stable self-assembled nanogels through a complex network of hydrophobic interactions. Carborane can be used to achieve efficient boron neutron capture therapy (BNCT) 1 because every molecule of this material is capable of delivering a high dose of boron. BNCT is a cellselective radiation technique that can be used to treat cancer.2 In terms of its therapeutic application, BNCT involves the use of α-particles and lithium nuclei, which are generated by the release of low-energy thermal neutron irradiation from boron via the boron neutron capture reaction. The energy emitted from the nuclei can lead to cell destruction, bouncing out up to 10¯m.1 The bouncing range of this technique corresponds to the size of a single cell, suggesting that BNCT could be used to selectively kill specific cells at the irradiated site without injuring normal tissues, if boron could be selectively delivered to tumor cells. In light of its therapeutic potential for the treatment of cancer, BNCT has been applied to a variety of malignant tumors, including melanoma 3 and glioblastoma, 4 where invasive techniques are generally poorly tolerated. The success of BNCT is dependent on the effectiveness with which highly concentrated 10 B particles can be delivered to cancer cells. 5 The development of effective boron carrier systems capable of increasing the therapeutic value on BNCT are therefore highly desired. 68 Herein, we reported the development of carborane-bearing polysaccharides, which undergo an efficient self-assembly process in water to form highly integrated boron clusters (Figure 1). Carborane shows high levels of hydrophobicity, thermal stability, and chemical stability. 912 The partial grafting of hydrophilic pullulan with carborane resulted in the formation of self-assembled nanogels through a series of hydrophobic interactions between the carboranes. It is envisaged that the integrated boron clusters formed in this way will show higher neutron capture efficiency than conventional polymer-based boron agents.Amphiphilic polysaccharides such as cholesterol-bearing pullulan (CHP) form stable physically crosslinked nanogels in water through hydrophobic interactions.1316 Self-assembly strategies can be used to form various functional nanogels. As shown in Figure 2, carborane-bearing pullulans (CAPs) were