Three new alkaline earth-zirconium oxalates M 2Zr(C 2O 4) 4· nH 2O have been synthesized by precipitation methods for M=Ba, Sr, Ca. For each compound the crystal structure was determined from single crystals obtained by controlled diffusion of M 2+ and Zr 4+ ions through silica gel containing oxalic acid. Ba 2Zr(C 2O 4) 4·7H 2O, monoclinic, space group C 2 / c , a = 9.830 ( 2 ) , b = 29.019 ( 6 ) , c = 9.178 ( 2 ) Å , β = 122.248 ( 4 ) ° , V = 2214.2 ( 8 ) Å 3 , Z = 4 , R = 0.0427 ; Sr 2Zr(C 2O 4) 4·11H 2O, tetragonal, space group I 4 1 / acd , a = 16.139 ( 4 ) , c = 18.247 ( 6 ) Å , V = 4753 ( 2 ) Å 3 , Z = 8 , R = 0.0403 ; Ca 2Zr(C 2O 4) 4·5H 2O, orthorhombic, space group Pna2 1, a = 8.4181 ( 5 ) , b = 15.8885 ( 8 ) , c = 15.8885 ( 8 ) Å , V = 2125 ( 2 ) Å 3 , Z = 4 , R = 0.0622 . The structures of the three compounds consist of chains of edge-shared MO 6(H 2O) x ( x = 2 or 3) polyhedra connected to ZrO 8 polyhedra through oxalate groups. Depending on the arrangement of chains, the ZrO 8 polyhedron geometry (dodecahedron or square antiprism) and the connectivity, two types of three-dimensional frameworks are obtained. For the smallest M 2+ cations (Sr 2+, Ca 2+), large tunnels are obtained, running down the c direction of the unit cell, which can accommodate zeolitic water molecules. For the largest Ba 2+ cation, the second framework is formed and is closely related to that of Pb 2Zr(C 2O 4) 4· nH 2O. The decomposition at 800°C into strontium carbonate, barium carbonate or calcium oxide and MZrO 3 ( M=Sr, Ba, Ca) perovskite is reported from thermal analyses studies and high temperature X-ray powder diffraction.