The solubility product is an important value characterizing the properties of slightly soluble compounds and is widely used in chemistry practices. It is a special case of the equilibrium constant for reactions of solid substance solution, which allows calculating a number of other thermodynamic parameters of the process. The present paper studies for the first time the effect of solution acidity in hydrochloric and perchloric acids on the solubility product of the following tellurites of rare earth elements: La-2(TeO3)(3), Y-2(TeO3)(3), and Sc-2(TeO3)(3). It is proven that the solubility product and the solubility itself of La-2(TeO3)(3) have higher values, followed by Sc-2(TeO3)(3) and Y-2(TeO3)(3). The values of the La-2(TeO3)(3) solubility product are closer to those of tellurites of the lanthanides Ce, Pr, and Nd compared to those of Y-2(TeO3)(3) and Sc-2(TeO3)(3). The close values indicate that they are analogues to the IIIb group of the Periodic Table.