Аннотация:The crystal structure of LaCaCuGaO5 has been investigated by single crystal X-ray analysis. It crystallizes with orthorhombic symmetry, space group C-2v(22) - Ima2, a = 15.8467, b = 5,5077, c = 5.3188 angstrom, Z = 4. LaCaCuGaO5 belongs to the mineral Brownmillerite showing layers of corner connected CuO6 octahedra linked by GaO4 tetrahedra. The La3+ and Ca2+ ions are distributed statistically over one crystallographic point position.