The newly found compounds RE0.65-0.7B12Si3.03 (RE = Y, Gd-Lu) show a layered structure, where boron icosahedra are interconnected into a two-dimensional Kagome lattice. The compressibility of this anisotropic structure is studied with Gd as a representative by X-ray diffraction. The structure is stable up to 27 GPa and shows a large volume bulk modulus of 212(7) GPa. Boron layer is a two-dimensional rigid framework and the unit cell is easier to be compressed between them. In addition, a sharp and pressure independent vibrational mode, which corresponds to the degenerate rotation of the icosahedron, was found by Raman measurement. (C) 2003 Elsevier B.V. All rights reserved.