Na-doped brownmillerite oxides La1-xNaxSrMn2O6 (x = 0, 0.1, 0.2 and 0.3) were synthesized by the solid state reaction method at high temperature. The structural and magnetic properties of the samples were investigated by X-ray diffraction and magnetization experiments. The results from X-ray diffraction analysis showed that all samples were single phase and crystallized in the orthorhombic system, with space group Pnma. This structure can be described as an oxygen-deficient perovskite, resulting in a sequence of regular alternating layers of corner-sharing BO6 octahedra (O) and BO4 tetraedra (T) according to axis b. The results from magnetization versus temperature measurements in a magnetic applied field of 0.05 T indicated that the samples underwent a paramagnetic ferromagnetic transition with decreasing temperature. The Curie temperature T-c decreased from 365 to 345 K with Na content. An electronic phase separation model considering the formation of ferromagnetic clusters in the antiferromagnetic matrix was proposed to interpret the observed magnetization results for the Na-substituted samples. Overall, the present study provided an effective approach to achieve new functional materials based on naturally occurring layered systems such as La1-xNaxSrMn2O5+delta, for possible application in the spintronics industry. (C) 2015 Elsevier B.V. All rights reserved.