In situ x-ray diffraction experiments of the fluorinated fullerenes, C60Fx (x = 0, 36 and 48) at high temperatures have been undertaken. The structural phase transformation of C60F48 was observed at about 358 K. It was also found that the lattice parameters of the low temperature phase of C60F48 show anomalous change at about 310 K. The thermal expansion coefficients of the fluorinated fullerenes were determined by using the change of the lattice parameters with temperature.