Performic acid was synthesized in a packed bed microstructured reactor in the presence of a cation exchange resin as a heterogeneous catalyst. The advantages of a cation exchange resin catalyst over a liquid catalyst (e.g. sulfuric acid) include decreased problems of corrosion and catalyst separation. Two cation exchange resins, Dowex 50Wx8 and Dowex 50Wx2, were selected and first tested in a batch process. The activity, life time, different size and crosslinking of the cation exchange resin catalyst in the formation of performic acid, in the batch process, were studied. According to the batch experiment results, Dowex 50Wx8 was preferred over Dowex 50Wx2 and packed in the reactor. Performic acid was synthesized continuously, at different temperatures, catalyst concentrations, and residence times. Increase in temperature and catalyst concentration accelerated the performic acid formation rate. This solid catalyst represented high activity which makes it possible to synthesize high concentration of performic acid in a short residence time. (C) 2011 Elsevier B.V. All rights reserved.