The Beckmann rearrangement of cyclohexanone oxime in oleum as a fast exothermic reaction model is carried out in an adiabatic multiphase microchemical system. A severe coalescene is observed due to the high viscosity of the rearrangement mixture, which decreases the reaction rate and selectivity. Gas agitation is introduced into the microsystem to enhance the reaction by reducing the coalescene and providing an evaporation space to carry away reaction heat. The effects of gas agitation on dispersion performance and mass-transfer rate have been investigated. The acid droplets diameter ranges from about 44 to 20 mu m, decreasing with the increase of the gas flow rate. The overall volume mass-transfer coefficient in the microsystem ranges from 0.16 to 0.74 s-1, 1.5-3.8 times larger than that without gas agitation. The reaction performance is evaluated under different conditions and better conversion and selectivity are obtained. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 2724-2730, 2014