We report here the pressure dependence of the electrical resistivity and magnetic susceptibility of polycrystalline Ce 0.6Y 0.4FeAsO 0.8F 0.2 superconductor in the temperature range 4 K to 300 K up to 8 GPa. In-situ high pressure-low temperature x-ray diffraction was performed at 8 K up to 32 GPa using synchrotron x-rays with helium pressure medium. The results show that the applied pressure slightly increases the T c up to 1 GPa and then it decreases on further pressure increase. The reduction of superconducting transition temperature occurs with a transition to a collapsed tetragonal phase and may be associated with a possible valence change of Ce. © 2012 American Institute of Physics.