We have performed X-ray powder diffraction measurements in a mixed valence compound of Fe 2 BO 4 using synchrotron radiation. The diffraction patterns obtained at several temperatures between 85 and 386 K were analyzed by the Rietveld method. The monoclinic–orthorhombic transition, ascribed to charge-ordering of Fe 2 + and Fe 3 + ions, was confirmed by the temperature dependence of the monoclinic angle β . No superlattice reflection due to the charge-ordering was detected. The temperature dependences of the lattice parameters show anomalies around 270 K as well as the monoclinic–orthorhombic transition temperature of 327– 347 K . The structural change around 270 K is attributable to the onset of the partial charge-delocalization.