The compressional behaviour of a natural kyanite, (Al 1.99 Fe 0.01 )SiO 5 , has been investigated to about 17.5GPa at 300K using a diamond-anvil cell and synchrotron X-ray diffraction. The pressure–volume data fitted to the third-order Birch–Murnaghan equation of state (EoS) yield an isothermal bulk modulus (K 0 T ) of 192±6GPa and pressure derivative (K0T′) of 6±1. When K0T′ is fixed as 4, the derived K 0 T is 201±2GPa. These values are in excellent agreement with most experimental determinations in the literature. Consequently, it can be concluded that the compressibility of kyanite under high pressures has been accurately constrained.