The present work deals with the synthesis of nanostructured MgO from different organic precursors, by a facile precipitation method as catalysts for the decontamination of Malathion (stimulant of chemical warfare agents) (VX) and orange G as organic pollutants. The as-prepared nanoparticles were obtained by thermal decomposition of the oxalate, tartarate, citrate, succinate, malate, malonate and glycinate precursors at ≈650°C and were characterized by thermal analysis, FTIR, X-ray diffraction, high resolution transmission electron microscope (HRTEM) and absorption spectra. The morphology and crystal sizes were found to be highly affected by the starting organic precursors. The results revealed that the prepared inexpensive magnesium oxides have high potential as catalysts for photo degradation of both Malathion and orange G from water samples. Inhibitory activity against Breast Carcinoma MCF-7 cell line was detected using some selected nanosized MgO and compared to that of Vinblastine as a standard drug.