The variation of crystal structure types of Mgx/2Li1-xIO3 with composition and temperature has been investigated by the methods of DTA and X-ray powder diffraction both at high and room temperatures. A new type of continuous solid solutions has been found in the entire region of the binary system Mg(IIO3)2·LiIO3.For the solid solutions rich in LilO3, the crystal lattice is distorted in the x-y plane with the increasing concentration of Mg(IO3)2, While the space group changes from P63 to P1121. At the composition 3Mg(IO3)2·7LiIO3, the lattice distortion reaches a maximum,γ=120o22′. With further increasing of the concentration of Mg(IO3)2, the lattice distortion is reduced, and at the composition Mg(IO3)2·LiIO3) the space group turns back again to P63.For the solid solution rich in Mg(IO3)2, the lattice is distorted along the z axis, and has been found to be made of unit cells of heterogeneous parameters c (the effect is most prominent at the composition about 20-30mol% LiIO3). But with increasing temperature, the crystal lattice gradually changes back to unit cells with a uniform parameter.It seems probable that the lattice distortions in the solid solutions are caused by vacancies. The heterogeneous distribution of vacancies results in inhomogeneous parameters c, and it is also due to the presence of vacancies that alters the crystal fields around the anion group, causing the displacement and rotation of IO3- with the result that the lattice is distorted along x-y plane.