(Bi 0.5Sr 0.5)(Fe 0.5Mn 0.5)O 3 crystallizes in a rhombohedral structure, with space group R3c, where the cations Bi 3+/Sr 2+ and Fe 3+/Mn 4+ occupy 6a and 6b sites respectively. Neutron diffraction, Mössbauer and magnetization measurements confirm long range antiferromagnetic ordering of the Fe 3+ and Mn 4+ moments at T N (226 K). Below T N, this oxide exhibits a cluster glass behavior and at low temperatures (∼30 K) a spin glass state is observed. The complex magnetic behavior is attributed to cation disorder in the system. Magnetic properties of this oxide are compared with those of the isostructural Bi 0.5La 0.5Fe 0.5Mn 0.5O 3 where both Fe and Mn ions exist in trivalent state. © 2012 The Royal Society of Chemistry.