A potassium cesium iron zirconium phosphate, KCsFeZrP₃O₁₂, was synthesized by simple solution method for the first time. Powder X-ray diffraction analysis confirmed that the compound crystallizes in cubic langbeinite structure (space group: P2₁3) with the cell parameters of a = 10.103 (2) Å and V = 1031 ų. Fourier transform infrared spectrum showed the stretching and bending vibrational bands of phosphate tetrahedra. Energy dispersive X-ray analysis proved the presence of elements. Leachability of a powder specimen was studied by MCC-5 test for a period of one month. Inductive coupled plasma and atomic absorption spectroscopic results revealed the negligible leaching of cesium. The normalized mass loss of potassium, iron, zirconium and phosphorous were found to be in the order of 10⁻⁴–10⁻³ g/m², 10⁻⁶–10⁻⁴ g/m², 10⁻⁵–10⁻³ g/m²and 10⁻⁴–10⁻³ g/m² respectively. For comparison, a cesium zirconium phosphate (CsZr₂P₃O₁₂) with the sodium zirconium phosphate structure was synthesized, and its leach rates of zirconium and phosphorous were comparable to those of the langbeinite phase. The cesium leach rate was negligible for both compounds.