We investigate the effect of ionic size variation on the electrical and thermodynamic properties in a series of Pr_0.7Ca_0.3−xSr_xMnO₃ (PCSMO) samples. The increase in Sr content results in an increase of the unit cell volume, as a bigger Sr²⁺ ion replaces the smaller Ca²⁺ ions. Resistivity measurements show that the increase in the Sr content also results in the induction of a metal–insulator transition (T_MI), which increases with increasing Sr content. The activation energy (E_a), calculated from the resistivity data, decreases with increasing Sr content confirming the metallic character. The effect of the magnetic field on resistivity and specific heat has also been studied.