Crystallographic features of Rhenium disilicide have been examined by powder and single-crystal X-ray diffractometry with a synchrotron radiation. The chemical composition of the compound is determined as Re4Si7 (ReSi2-x, x = 0.25) from lattice constants and specific density determined. The structure is defined as a vacancy ordered structure with the space group of Cm. The positions of the constituent atoms in the structure have been refined. The positions of silicon atoms apparently shift from the ideal positions of the C11b structure which is the structure without containing structural vacancies.