The application of microreaction technology has the potential to chemical processes. It is therefore of great interest to investigate the operating efficiency of a multiphase process such as the alkylation of phenylacetonitrile in a microreactor and to compare the performance to a batch reactor. The undeniable advantages of continuous microreactor systems for this process were demonstrated. Furthermore, the influence of the organic to aqueous phase ratio in the microreactor was investigated. A model of the reaction course was formulated based on experimental data. This model was used in the analysis a rid modeling of the alkylation process in a microreactor and found to be adequate. The optimal microreactor performance conditions were determined using the numerical optimization technique (Harrington's desirability function) and confirmed by experiments.