Brownmillerite-type oxides Ba(2)In(2-x)Mn(x)O(5+x) (x = 0.1-0.7) have been prepared and characterized. Magnetic measurements indicate that manganese in as-prepared samples is substituting predominantly as Mn(5+) for all values of x with observed paramagnetic spin-only moments close to values expected for two unpaired electrons. Electron paramagnetic resonance measurements indicate that this Mn(5+) is present in a highly distorted tetrahedral environment. Neutron diffraction structure refinements show that Mn(5+) occupies tetrahedral sites for orthorhombic (x = 0.1) and tetragonal (x = 0.2) phases. For Mn ≥ 0.3 samples, neutron refinements show that the phases are cubic with disordered cations and oxygen vacancies. The colors of the phases change from light yellow (x = 0) to intense turquoise (x = 0.1) to green (x = 0.2, 0.3) or to dark green (x ≥ 0.4). Under reducing conditions, Mn(5+) is reduced to Mn(3+), and Ba(2)In(2-x)Mn(x)O(5+x) phases become black Ba(2)In(2-x)Mn(x)O(5) phases still with the brownmillerite structure.