The samples belonging to La 1−x Sr x MnO 3 series, prepared by combustion route without using fuel, exhibit crystal structural phase transition with the change in Sr content. Less than 40 mol% Sr is partially substituted in the crystal structure of LaMnO 3 . The structural phase transition from rhombohedral to cubic, cubic to tetragonal, and tetragonal to orthorhombic takes place on 40, 60, and 80 mol% addition of Sr. The highest electrical conductivity in La 0.4 Sr 0.6 MnO 3 is understood to be due to the maximum concentration of polaron. The polarons are formed due to the conversion of Mn 3+ to Mn 4+ so as to achieve electroneutrality after substitution of Sr 2+ for La 3+ .