Single crystals of pure and Cd2+ doped potassium sulfate were grown from aqueous solutions by the slow evaporation technique. From nutrient solutions with a CdSO4 concentration of 4wt.% crystals containing 0.014wt.% dopant concentration could be obtained. The X-ray diffraction patterns of powdered crystals confirmed their crystal structures for both cases. Thermal analysis of pure crystals shows that the alpha-beta phase transformation peak around 580 deg C is superimposed with spurious effects, while for Cd2+ doped crystals this is not the case. The thermal hysteresis of the phase transition is 8 K for undoped K2SO4 and is reduced to 3.5 K for K2SO4:Cd2+. Compared to undoped crystals, the optical transmittance of Cd2+ doped crystals is higher. Comment: 5 pages, 6 figures