<p>This article presents experimental and theoretical data on the investigation of the electrical transport characteristics of strontium ferromolybdate with different structural states of grain boundaries. These samples demonstrate non-monotonic behavior of the electrical resistivity in the temperature range of 4.2–300&#xa0;K, which leads to the presence of an inflection points (<i>T</i>_inf) with a minimum electrical resistivity. It has been established that the process of annealing in a vacuum with residual oxygen pressure of the magnetic semiconductor Sr₂FeMoO_6−δ substantially changes the structurally inhomogeneous state of grain boundaries, which significantly affects the scattering mechanisms of free charge carriers. It is shown that the dominant scattering of electrons in the high-temperature region <i>T</i>_inf &lt; <i>T</i> ˂ 300&#xa0;K is due to a combination of electron – single magnon and electron-phonon interactions. In the low-temperature region at 4.2 &lt; <i>T</i> ˂ <i>T</i>_inf, under conditions of structurally-inhomogeneous state of grain boundaries, effects of the weak localization are realized due to the quantum interference of conduction electrons. Our work sheds new light on the applications of polycrystalline magnetic semiconductors with structurally inhomogeneous grain boundaries in spintronics and functional sensors of resistive type.</p>