Abstract Polymer microchannel chips (100 μm width × 20 μm depth) integrated with electrodes were fabricated and applied to a one-step electrochemical cyanation reaction of pyrene (PyH). An acetonitrile solution of PyH containing tetrabutylammonium perchlorate and an aqueous NaCN solution were brought into the chip by pressure-driven flow, PyH was then oxidized at the working band electrode in the channel (1.5 V vs Ag). Under the optimum conditions, 1-cyanopyrene (PyCN) was produced very efficiently in the microchannel: 61% yield. It was also confirmed that, although 1,3-dicyanopyrene (Py(CN)2) was produced by bulk electrolysis (14% yield), its yield decreased to 4% in the microchip, with the PyCN/Py(CN)2 yield ratio being 2.9 or 15.3 for the bulk or chip experiments, respectively. In the case of an oil/water interfacial reaction system, a propylene carbonate solution of PyH and an aqueous NaCN solution were introduced to the channel, where an electrochemical cyanation reaction of PyH analogous to that mentioned above was conducted. The interfacial reaction in the microchip was successful and the yield of PyCN as the sole product was shown to be controlled by both the flow rate and the electrode position in the chip. In-situ space-resolved absorption spectroscopy of the electrochemical intermediate in the channel chip was also conducted to allow discussion of the reaction mechanisms.