Oxygen-stoichiometric La 0.5 Sr 0.5 M 0.5 Ti 0.5 O 3 (M ¼ Mn, Fe) perovskites and the corresponding reduced specimens, of La 0.5 Sr 0.5 M 0.5 Ti 0.5 O 3-d composition, have been prepared and characterized by x-ray diffraction and neutron powder diffraction (NPD), in complement with thermal analysis, electrical conductivity, and thermal expansion measurements. NPD data show that these perovskites are all orthorhombic, space group Pbnm (No. 62). The total reduction of M 3þ to M 2þ in the reduced phases is accompanied with the occurrence of oxygen vacancies, which was confirmed by thermogravimetric analysis (TGA). Above room-temperature, these phases undergo two structural phase transitions studied in situ from NPD data; the former to a tetragonal (I4/mcm) structure, and the second one to a cubic (Pm-3m) phase. All the oxides display a semiconductorlike behavior with a maximum conductivity value of 15 SÁcm