Sodium zirconium phosphate (NZP) is a potential material for immobilization of nuclear effluents. The existence of cesium containing NZP structure was determined on the basis of crystal data of solid solution. It was found that up to similar to 9.0 wt% of cesium could be loaded into NZP formulations without significant changes of the three-dimensional framework structure. The crystal chemistry of Na1-x Cs (x) Zr2P3O12 (x = 0.1-0.4) has been investigated using General Structure Analysis System programming. The CsNZP phases crystallize in the space group R-3c and Z = 6. Powder diffraction data have been subjected to Rietveld refinement to arrive at a satisfactory structural convergence of R-factors. The unit cell volume and polyhedral (ZrO6 and PO4) distortion increase with rise in the mole% of Cs+ in the NZP matrix. The PO4 stretching and bending vibrations in the infrared region have been assigned. SEM, TEM, and EDAX analysis provide analytical evidence of cesium in the matrix.