Mineral-like magnesium-potassium-phosphate (MPP) compound samples were synthesized during the immobilization of a high level waste (HLW) simulator. The phase composition and structure of compounds were studied and their physico-chemical properties, including mechanical and thermal stability, were determined. The high hydrolytic stability of the MPP compound was established: the differential leaching rates at the 90th day of contact with water under 23 0С were for 137Cs - 4.6∙10-7, 90Sr – 9.7∙10-7, 239Pu - 3.7∙10-10 and 241Am - 9.6∙10-10 g / (cm2 / day). The leaching of radionuclides during the first 2 weeks was caused by the dissolution or washing out from the surface of the compound, when the experiments were being continued for 90 days the leaching was done by the depletion of the surface layer. The permanence of the phase composition, structure, and hydrolytic stability of MPP compound irradiated by an electron beam (absorbed dose -1 MGy) was established, it means that the MPP compound is stable to radiation. The quality profile of MPP compound corresponds to current regulatory requirements, which make possible to consider the compound as perspective material for industrial solidification of HLW.