Crystallographic, magnetic, and magnetoresistive properties of heterosubstituted lanthanum—strontium manganite ceramic samples doped with Fe are studied. The samples for investigation are fabricated by sintering of powders synthesized by sol—gel method. As shown, the lattice unit-cell volume decreases with the growing of Fe content that points on partially isovalent substitution of Mn$^{3+}$ by Fe$^{3+}$. As established, the La$_{0.77}$Sr$_{0.23}$Mn$_{1-y}$Fe$_{y}$O$_{3}$ samples with $y \leq 0.04$ are ferromagnetic, and the samples with $y > 0.04$ are paramagnetic at room temperature. The character of changes of both the magnetization and the Curie point with the change of $y$ is investigated. As shown, the Curie temperature of the La$_{0.77}$Sr$_{0.23}$Mn$_{1-y}$Fe$_{y}$O$_{3}$ samples almost linearly decreases with the increasing of the Fe content. Obtained results allow predicting reliably the magnetic parameters of La$_{0.77}$Sr$_{0.23}$Mn$_{1-y}$Fe$_{y}$O$_{3}$ system in the range of small $y$ values ($y = 0-0.1$) that is important for the application of these materials in medicine, particularly for using them in magnetic fluids as the inductors of hyperthermia.