The compressibility of zircon and reidite (ZrSiO4) was investigated by powder X-ray diffraction (XRD) up to 20 GPa using a synchrotron radiation source. Reliable equations of state for zircon and reidite were obtained using a diamond anvil cell (DAC) coupled with yttrium-aluminum-garnet (YAG) laser-heating. Samples were heated with the laser at each pressure increment to relax deviatoric stress. XRD measurements were carried out at 300 K using an angle-dispersive technique. Data refinements yield third-order Birch-Murnaghan equations of state parameters: the bulk modulus K0 = 205(±8) GPa when the first pressure derivative of the bulk modulus, K′0, is fixed at 4 for zircon, K0 = 392(±9) when K′0 is fixed at 4 for reidite. The volume reduction of the phase transition from zircon to reidite is about 10%. The tentative phase boundary between zircon and reidite is located at about 10 GPa.