Selective oxidation of phenol with hydrogen peroxide over titanium silicalite-1 (TS-1) was performed using two types of catalytic microreactor: a packed bed microreactor and a catalytic wall microreactor. The reaction rates were markedly faster in both microreactors than in flasks due to improvement of the contact efficiency between reactant and catalyst. However, using a packed bed microreactor, phenol conversion and yields of benzenediols decreased gradually with time course. Therefore, we developed a catalytic wall microreactor in which catalyst elements could be exchanged easily. Use of this new catalytic wall reactor suppressed catalyst deactivation. In addition, the regioselectivity of hydroxylation, i.e., the molar ratio of para-diol (hydroquinone)/ortho-diol (catechol) changed remarkably. A higher degree of para-selectivity was achieved with the wall type reactor than the packed bed type reactor. (c) 2007 Elsevier B.V. All rights reserved.