The structural relationships in FeF2 have been studied under pressure up to 320 kbar and 25 ¿C by use of the diamond anvil pressure cell. In situ X-ray diffraction analysis shows that at about 50 kbar, FeF2(I) with rutile structure transforms into FeF2(II) of distorted fluorite structure and at about 250 kbar FeF2(II) further transforms into FeF2(III) with a hexagonal unit-cell structure. The zero-pressure density increase for the transition FeF2(I) →FeF2(II) is ~8%, and the density increase for FeF2(II) →FeF2(III) at 320 kbar is ~5%, if the number of formula units per unit cell is assigned at 2 for the hexagonal unit cell.