Dy2Ti2O7 with the pyrochlore structure shows a spin ice transition at about 1 K. The Dy3+ ion in this compound has an effective spin Seff=1/2. The Dy ions reside on the vertices of corner‐linked tetrahedra. Due to a strong single‐ion anisotropy, the ground state of Dy3+ is well expressed by an Ising doublet with local 〈111〉 quantization axes. We measured the x‐ray diffraction for a Dy2Ti2O7 powder sample between 0.15 K. and 20 K. The lattice spacing increases drastically between 1.5 K and about 1 K, with decreasing temperature. The lattice spacing of the (222) diffraction is considerably larger than the other directions.