Oxidation of 2-methylnaphthalene was performed as a model reaction under severe conditions in order to develop operation strategies for highly efficient oxidation of aromatics. A microreactor system was used which allows oxidation reactions to be carried out under conditions which cannot be realized by conventional approaches. Owing to the good heat transfer performance and rapid mixing technology, it is possible to increase reaction temperature and add oxidants at considerably higher concentrations than in traditional semibatch processes. The selectivity of the desired product, 2-methyl-1,4-naphthoquinone, increased to 50% via the suppression of consecutive side reactions by controlling a short residence time at a high temperature. It was clarified that microreaction systems provide a new route to precisely control the oxidation of aromatics.