The detection, removal and reduction of hydrogen peroxide and organic peroxides is of significant importance for its increasing application in the areas of environment, food, electrochemistry and clinical laboratory. Herein the dissociative adsorption behavior of H2O2 and organic peroxides on ultrathin magnesia (0 0 1) films deposited on transition metal is uncovered for the first time by employing periodic density-functional theory calculations with van der Waals corrections. Splitting of H2O2 on bulk MgO(001) is highly endothermic process with activation barrier 1.85 eV, indicating it is extraordinarily difficult to dissociate H2O2 on pristine MgO(0 0 1). The H2O2 is dissociated smoothly and reduced to surface hydroxyls on MgO(0 0 1)/TM, and the dissociative adsorption energies of all the considered fragmentation configurations are substantially negative, demonstrating dissociation and reduction of H2O2 is thermodynamically favorable. The mechanism of reactivity enhancement for energetically and dynamically favorable decomposition of H2O2 on supported magnesia is elucidated by characterizing the geometric structures and electronic properties. The fragmentation and reduction of diethyl peroxide and peroxyacetone are also studied to reveal the catalytic activity of ultrathin magnesia toward splitting organic peroxides. The results are wished to provide useful clue for detecting and reducing hydrogen peroxide and organic peroxides by employing oxide-metal hybrid nanostructure.