Strontium-doped lanthanum manganite La1-xSrxMnO3 (LSM) is characterized by hexagonal-rhombohedral distorted perovskite-type structure, deriving from the ideal cubic symmetry through rotation of the [MnO6] octahedra around the ternary axis. The extent of distortion and unit cell volume depend on Sr content. The linear variation of the unit cell volume, observed in the compositional range 0.1 less-than-or-equal-to x less-than-or-equal-to 0.5, can be effectively used for determining the stoichiometry of LSM. A procedure for the quantitative analysis of segregated impurities (La2O3 and Mn3O4) based on X-ray powder diffraction analysis, has also been developed.