In this report, SrFeO3 photocatalyst powder was synthesized by a high temperature solid state reaction method and the size of the particle was reduced with a high energy ball milling machine. The morphology, crystalline structure, particle size and size distribution of obtained samples were characterized by energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), UV-vis spectrometer, scanning electron microscope (SEM), and transmission electron microscopy (TEM). Photocatalytic activity of the prepared samples was investigated by photodegradation of methylene blue (MB). The obtained results show that the SrFeO3 sample works as photocatalyst and by reducing the particle size using high energy ball milling method for 5 h milling, particles with 19-25 nm crystallite size exhibit maximum activity due to larger surface area. The photocatalytic activities of the powders were investigated and kinetics of reaction was modeled by using high performance liquid chromatography (HPLC) and Mass spectroscopy. Photocatalytic activities of these powders increase with decreasing particle size. (C) 2010 Elsevier B.V. All rights reserved.