Abstract The volume compression of a-LiIO_3_ has been studied by X-ray diffraction in a diamond anvil cell up to 23.0GPa at room temperature. The anisotropic compression of lattice was observed. The ratio of c/a of parameters decreased with a rate of -6.187x 10**(-3)/GPa with pressure. The bulk modulus of normal pressure and its first pressure deviative have been determined to be equal to 39.2 and 3.787GPa respectively. At high pressure and high temperature, hexagonal a-LiIO_3_ transformed to a tetragonal phase. The structure was the same as quenching-releasing pressure phase, i.e., the E phase.