Microreactors are effective tools for the intensification of fast exothermic chemical reactions. In this work, we focus on the kinetics study of a microreacting process to provide a deeper understanding of the transport and reaction performance within microreactors. An experimental setup incorporating an online kinetic measurement method was developed based on the temperature-conversion relationship in the cyclohexanecarboxylic acid-oleum reaction - a crucial reaction for the preparation of epsilon-caprolactam. The reactant conversion was successfully recorded in a reaction time of less than 1.0 s, and it was determined that the reaction rate was mainly controlled by the mixing of reactants. The mass transfer coefficient in the microreactor reached 10(-4) m/s, and the observed selectivity of the main-product was higher than 97%. Based on the experimental results, a single-droplet model was developed to establish a better understanding of the temperature and concentration distributions in the reacting system as well as analyze the effect of drop size on main-product selectivity. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.