Single crystals of CaIrO 3 were prepared via flux growth method. Crystal structure parameters, including the anisotropic displacement parameters, are determined based on a single-crystal X-ray diffraction experiment. The unit-cell dimensions are a = 3.147(2), b = 9.866(6), and c = 7.302(5) A. The structure is a three-dimensional dense structure with small vacant spaces. The CaIrO 3 structure can be described as a pseudo-one-dimensional oxide and is compared with Ca 4 IrO 6 structure. The IrO 6 octahedra are significantly distorted, in contrast to other octahedral Ir 4+ compounds. The O-O distances for faces and edges shared between polyhedra are shorter than other non-shared edge distances. These effects are explained by Pauling’s rules and occur to decrease the repulsion between the cations. Thermal vibrations of Ca and Ir atoms are significantly anisotropic. Thermal vibrations of Ca and Ir atoms are restricted in orientation toward the shared face, shared edges, and shortest cation-cation directions. The single-crystal experiment shows that CaIrO 3 crystals grow fastest along the a axis and that they assume a prism or needle shape. Strongly preferred orientation of such prism shaped CaIrO 3 -type post perovskite MgSiO 3 crystals may develop under the shear flow in the Earth’s mantle.