The effect of gadolinium substitution by barium on the crystal structure, microstructure, magnetic and electrical properties of Gd1−XBaXMnO3 (x = 0.0; 0.15; 0.18; 0.25) prepared by the solid-state reaction method has been studied. An increase in the concentration of barium to x = 0.18 leads to a critical decrease in the concentration of Mn3+ ions involved in the distortion mechanism and changes in the structural order (Jahn-Teller transition). The porosity of the samples increases and average the grain size and decreases as the concentration of barium increases. The electrical conductivity of Gd1−xBaxMnO3 increases up to 1.5 times compared to the initial material when the concentration of barium increases to x = 0.25. All manganites have TN = 42 K. The Curie temperature increases and changes the sign from negative to positive as the substitution level increases. For the first time, a phase diagram of the evolution of structural, magnetic and electrical properties when replacing Gd with Ba is presented. The evolution of magnetic and electrical properties of manganites is associated with structural distortions of the crystal lattice caused by the substitution of gadolinium with barium.