Nano Mn3O4 particles were synthesized by the combustion of gel from polyvinyl acohol (PVA) and tartaric acid (TA). Factors affecting on Mn3O4 formation such as the pH of solution, temperature of gel formation, mole ratio of TA:PVA, mole ratio of Mn:(TA:PVA), temperature of calcination were investigated. The structure of Mn3O4 particles were characterized by Differential Thermal Analysis, X- Ray Diffraction and Field Emission Scanning Electron Microscopy measurement. The results showed that single-phase Mn3O4 was smaller than 60 nm of average grain size. The nanostructured Mn3O4 was used to investigate the photocatalytic capacity under the visible light irradiation. The results indicated that Mn3O4 catalysts showed a rather high photocatalytic ability to decompose the organophosphorous pesticide: parathion. The intermediates coming from the photocatalytic degradation were identified by gas chromatography – mass spectrometer. The results showed that the intermediates of degradation reactions were not more toxic than the initial substances.Keywords: Nanostructured Mn3O4, tartaric acid, PVA, methyl organic, photocatalytic.