We report the crystallographic parameters of LaMnO3 obtained from X-ray diffraction data and electronic properties predictions using the density functional theory (DFT). LaMnO3 was prepared by the citrate precursor method (CPM). The initial solution was 0.1M of each cation and the citrate nitrate relation was one. The solution was dried at 373 K; the yielded foam was annealed at 873K and then was characterized by X-ray diffraction. Diffraction peaks show that the space group is R-3c (#167) with a ¼ b ¼ 5.523A ˚ and c ¼ 13.324A ˚ (rhombohedrally distorted perovskite). Structural results of the Rietveld method have a matching of 97% with that obtained from the Structure Prediction Diagnostic Software. DFT calculation reveals a half-metallic character and its magnetic moment is about 2.0 mB.