Two hybrid rare-earth double perovskites, (CH3NH3)2KGdCl6 and (CH3NH3)2KYCl6, have been synthesized by a solution evaporation method and their structures determined by variable temperature single crystal X-ray diffraction. The diffraction results show that at room temperature both perovskites adopt a rhombohedral structure with R 3m symmetry, as found previously for (MA)2KBiCl6, and lattice parameters of a = 7.7704(5) Å and c = 20.945(2) Å for (MA)2KGdCl6 and a = 7.6212(12) Å and c = 20.742(4) Å for (MA)2KYCl6. Both phases exhibit a rhombohedral to cubic phase transition on heating to 435 K for (MA)2KYCl6 and 375 K for (MA)2KGdCl6. Density functional calculations on the rhombohedral phase indicate that both materials have large direct band gaps, are mechanically stable and, in the case of (MA)2KGdCl6, could exhibit magnetic ordering at low temperatures.