Processes taking part during reaction of chlorides of 15 rare earth elements (yttrium, lanEthanum and all lanthanides except for promethium) with sodium orthophosphate in themelts based on NaCl-KCl equimolar mixture under inert atmosphere at 750 C. Phase comEposition and particle size distribution of the phosphates of rare earth elements (REE) formed was determined. The effect of the mole ratio of phosphate to REE on the composition and particle size of the phosphates formed was studied. Conditions required for the quantitative precipitating from the melt individual REE and a mixture of REE imitating the content of rare earth fission products in the spent nuclear fuels arriving for the reprocessing.