An efficient method has been developed for oxidative aromatization of 2-pyrazolines and isoxazolines into their corresponding 2-pyrazoles and isoxazoles under mild conditions. In this method, trans-3,5-dihydroperoxy-3,5-dimethyl-1,2dioxalane–NH Cl–HOAc was used as a novel and effective oxidant in water–MeCN at room temperature with good yields.