Powders with phase composition including syngenite K2Ca(SO4)2·H2O and/or calcium sulfate di-hydrate (gypsum) CaSO4·2H2O were synthesized from powder of calcium carbonate CaCO3 and water solutions of potassium hydrosulfate KHSO4 of various (0.5M, 1M and 2M) concentrations. Molar ratio of starting salt KHSO4/CaCO3=2 were used to provide formation of syngenite K2Ca(SO4)2·H2O. But when using 0.5M water solution of potassium hydrosulfate KHSO4 the phase composition of synthesized powder was presented by calcium sulfate dihydrate (gypsum) CaSO4·2H2O. When using 1M and 2M water solution of potassium hydrosulfate KHSO4 the syn-genite K2Ca(SO4)2·H2O was found as predominant phase in synthesized powders. According es-timations made from thermal analysis data when 1.0M and 2.0M water solutions of potassium hydrosulfate KHSO4 were used the content of calcium sulfate dihydrate (gypsum) CaSO4·2H2O in these powders were not higher then as 7.9 and 1.9 % respectively. Phase composition of products isolated from mother liquors via water evaporation consisted of syngenite K2Ca(SO4)2·H2O and potassium sulfate (arcanite) K2SO4. Synthesized powders can be used in preparation of biocom-patible bioresorbable materials with phase composition in the K2O‑CaO‑SO3‑H2O system; as matrix of thermo- or photo-luminescent materials; as components reducing the setting time and increasing strength of sulfate cements; in the fertilizing industry and also as a components of Martian regolith simulant.