Abstract Sr 2CuO 2(CO 3) was prepared at 1273 K and 0.01 MPa CO 2 partial pressure in a flowing gas of O 2CO 2 using a mixture of SrCO 3 and CuO powders as a starting material. The compound has a tetragonal structure with lattice constants a = 7.8045(1), and c = 14.993(1) A ̊ , and its space group is 14. The formula per unit cell is 8 Sr 2CuO 2(CO 3), and measured and calculated densities are D m = 4.71 g/cm 3, and D x = 4.81 g/cm 3, respectively. The crystal structure was refined by Rietveld analysis on X-ray powder diffraction and neutron powder diffraction data. The final residuals ( R F) were 4.31 and 4.27% for the X-ray and neutron data, respectively. The structure consists of deformed [CuO 6] octahedrons and layers of ordered triangular CO 3 groups. Sr atoms having eight near oxygen neighbors are between the [CuO 6] octahedrons and the CO 3 layers.