We prepared a new rare-earth compound, Eu9MgS2B20O41 (EMSBO), and characterized its structural and physical properties. EMSBO consists of triple-Kagomé-layer slabs separated by nonmagnetic ions and groups. Within each slab, intervalence charge transfer has been found to occur between the Eu2+ and Eu3+ Kagomé layers, a new channel for quantum fluctuation of magnetic moments. The measured magnetic susceptibilities and the specific heat capacity exhibit very similar features characteristic of quantum spin liquid behaviors observed in other materials.