Vibrant blue. crystals of Na4Mn0.5P0.5O5 were synthesized via a sodium hydroxide flux. The X-ray structural analysis showed that this sodium manganese(VII) phosphorous oxide crystallizes in air orthorhombic lattice with a = 8.967(3) Angstrom, b = 7.291(3) Angstrom, c = 8.090(3) Angstrom Pnma (No. 62); Z = 4. The manganese and phosphorus cations equally share one crystallographic site and are tetrahedrally coordinated, The (Mn,P)O-4 tetrahedra are held together by sodium cations,via Na-O bonds forming an ionic solid, [Na4O](2+)[(Mn0.5P0.5)O-4](2-). The synthesis, structure, thermal property and infrared spectroscopy of the title compound are presented in this paper.